Stan Wawrinka fought back to stun sixth seed Grigor Dimitrov and claim his biggest victory since having knee surgery in the Wimbledon first round.

The Swiss, a three-time Grand Slam champion, has dropped to 224th in the world and lost to Andy Murray in the first round at Eastbourne last week.

But he rallied to beat Dimitrov 1-6 7-6 (7-3) 7-6 (7-5) 6-4 on Centre Court.

Elsewhere, third seed Marin Cilic, last year’s beaten finalist, defeated Japan’s Yoshihito Nishioka 6-1 6-4 6-4.

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Wawrinka’s revival

Despite his successful career, Wawrinka has never made it further than the quarter-finals at Wimbledon.

He fell in the opening round last year to Russia’s Daniil Medvedev when he was hindered by his knee, and later opted to have surgery and end his season early.

He returned to the tour for the Australian Open in January, but ultimately had further surgery in February which kept him out until May.

Wawrinka began slowly against Bulgaria’s Dimitrov, who won the season-ending ATP Tour finals in November, but has struggled for form since.

Dimitrov let slip a 5-2 lead in the third set and Wawrinka muscled past him to record a first win over a top-10 player on grass.

It was a memorable day for the 33-year-old, as his partner Donna Vekic beat women’s fourth seed Sloane Stephens earlier.

“My goal was to fight and to focus on my game,” Wawrinka told BBC Sport.

“Grigor is a tough player and I knew I was nervous but I have been practising hard.

“I will do everything to be ready for the next match. When you win, it helps your body to recover.”

‘Devastating loss’ – analysis

John McEnroe, former Wimbledon champion on BBC Two

We saw guys lacking confidence for different reasons. Wawrinka is coming back from injury, but Dimitrov is inexplicable.

Dimitrov couldn’t handle the expectation, the pressure he put on himself.

When push comes to shove, he’s coming up empty. It’s a devastating loss considering he had opportunities to win it.

Querrey’s wedding dilemma

Also through is American Sam Querrey who beat Andy Murray on his way to the 2017 semi-finals.

Querrey, the 11th seed this year, had few problems as he saw off Australia’s Jordan Thompson 6-2 6-4 6-3.

The 30-year-old, who got married to Abby Dixon last month, said afterwards that he postponed his honeymoon plans to step up his grass-court preparations for Wimbledon.

“We went home for three days and flew over for Queen’s, if you count that as a honeymoon,” he said.

“I don’t think Abby does. Maybe at the end of the year, we will do a honeymoon somewhere close to where we live.”

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US Open champion Sloane Stephens and fifth seed Elina Svitolina were the biggest casualties on the opening day of the Wimbledon women’s singles.

The fourth-seeded American looked out of sorts in a 6-1 6-3 loss to world number 55 Donna Vekic from Croatia who caused problems with her big hitting.

Svitolina, from Ukraine, was beaten by German world number 57 Tatjana Maria.

Maria, one of a small number of mothers on the Tour, went through 6-7 (3-7) 6-4 6-1 after a late-night finish.

However, Caroline Wozniacki and Venus Williams were among the seeded players to go through.

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Australian Open champion Wozniacki, the second seed, needed 59 minutes to beat American Varvara Lepchenko 6-0 6-3.

Five-time winner Williams, who was beaten by Garbine Muguruza in last year’s final, made a slow start before beating Sweden’s Johanna Larsson in three sets.

Larsson, who had never won in her seven previous Wimbledon visits, won the opening set on a tie-break.

But Williams, 38, grew in confidence to win 6-7 (3-7) 6-2 6-1.

Vekic’s victory is her first over a top-five player and comes after first-round exits to Williams and Johanna Konta in the past two years.

“I always try to be aggressive,” she told BBC Sport.

“I struggled with my serve in the wind but hopefully I can improve. I played all the tournaments on grass coming here and that has helped me.”

The 2012 finalist Agnieszka Radwanska needed to save six match points before beating Romania’s Elena-Gabriela Ruse.

The Pole, who has been struggling with back problems, went on to win 6-3 4-6 7-5.

American 16th seed Coco Vandeweghe was hampered by injury as she bowed out to Katerina Siniakova of the Czech Republic.

The 26-year-old needed treatment on her ankle during the match and was visibly limping as Siniakova eventually wrapped up a 6-7 (3-7) 6-3 8-6 win in three hours and one minute.

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Serena Williams battled blustery conditions to reach the Wimbledon second round with a 7-5 6-3 victory over Dutchwoman Arantxa Rus.

Seven-time champion Williams, the 25th seed after having a baby in September, did not have it all her own way against the left-hander’s formidable forehand.

After winning the first set when Rus sent a forehand long, she had to fight back from a break down in the second.

Williams faces Tereza Smitkova or Viktoriya Tomova next.

More to follow.

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Imagine you’ve just finished your education and it’s now time for you to get a job.

On your first day, you may be assigned a mentor – an experienced and trusted colleague to advise and guide you.

For many of us, that mentor may take the form of “Janet from human resources” – a sweet parental figure in the office, but you probably won’t be chatting about last night’s Love Island.

Now imagine you are a young British tennis prospect and you discovered your mentor was going to be Andy Murray.

Well, that is exactly what happened to 19-year-old Katie Swan and 17-year-old Aidan McHugh.

The players recently signed to Murray’s management company, 77 Group, and the two-time Wimbledon champion is now guiding them through the early stages of their careers on the tour.

BBC Sport went to meet them between training sessions at Wimbledon the week before the 2018 Championships began.

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BBC Sport: Nice to meet you both! You are playing here at Wimbledon this year – Katie you have received a wildcard for the main draw, how did that feel?

Katie: Yeah, it’s an amazing feeling. When I played here in 2016 it was a great experience but I didn’t feel like I was really ready. But this year I feel much more prepared and that I can really give it a good go.

Have you decided what you might do with the prize money? Do you think you will treat yourself? (First round entrants receive £39,000 – win or lose.)

Katie: No, probably not! It will all go towards my coaching and travel. Being a professional tennis player is relatively expensive.

Aidan, (who will be playing in the junior boys championship), you seem to have a big brother/little brother relationship with Andy. He seems to comment on your Instagram a lot…and he’s pretty savage!

Aidan: Yeah, he does tend to tear into me with some of the comments. I don’t think there is any maliciousness in it though – it’s all sarcastic! Katie gets a nice comment every now and again off him but that’s just the way it is I guess.

Katie: Yeah he does just tend to abuse you!

What does this mentoring role involve, Katie?

Katie: Well if we need any help or advice with anything we just send him a text and he does everything he can to help. He is such a nice guy and he’s so easy to talk to so I definitely feel comfortable to text him when I need to. It’s really nice to have someone who has been there and done everything. He is a real inspiration to me.

How often do you speak to him?

Katie: We are in touch every couple of weeks. We did a team dinner last week in Eastbourne.

What do you talk about at a team dinner? Is there much tennis chat?

Katie: No, not much really. We were talking about Love Island. It’s a big topic right now!

Ahh yes, so who is your favourite couple?

Katie: Dani and Jack definitely!

Aidan: Yeah, for sure they are the strongest couple but there are others who have some good banter. It’s quite funny to watch.

Do you guys manage to fit in dating at all?

Katie: Well I’ve had a boyfriend for two-and-a-half years so we are going strong! He is also a tennis player [British player Joel Cannell] so he travels a lot too. We don’t see each other often but we make it work….Anyway, Aidan?!

Aidan: Ha! Yeah obviously, one good thing I would say is, you are playing with the same people every week so the boys and girls all know each other.

Katie: That’s a very political answer Aidan…

Aidan: Yeah I know what I’m doing, it’s not my first time answering that question.

Well navigated. So what is the best thing about being on tour?

Aidan: Getting to travel around the world I’d say.

Katie: Yeah, you get to see so many amazing places and meet interesting people and we are getting to do what we love

And what’s the worst thing?

Aidan: Travel and jet lag is also the downside.

Katie: Being away from home and missing my dogs is so hard. I have four of them. They are a good bunch!

Aidan: Yeah I’ve got a cat too – Oscar.

Is there anything you feel you are missing out on?

Aidan: Well, my friends from school have just finished so they’ve just gone on a massive three week holiday which is pretty nice for them.

Katie: Same. During the summer, my friends go travelling and go away together. It’s tough but I would much rather be here at Wimbledon.

Talk to us about tennis – what do you want to achieve in the game?

Katie: The end goal is winning Grand Slams, 100%. Short term though, I have just recently got my ranking up enough to be in the qualifying for the US Open in New York so I want to play my best tennis there.

Aidan: I’d say the same but getting to number one would be amazing too. Doing that takes so much consistency – you can’t just have a couple of good weeks, you have to be doing it the whole year. But right now, I am just trying to get my ranking up. I want to keep improving and do well at some of the ATP Challenger tournaments.

So as elite athletes, your fitness is key but we often read people your age feel a lot more pressure than previous generations about body image. Is that something that you have experienced?

Aidan: I have read a few things about this but I’d say we are quite lucky – we play a lot of sport and always have done from a young age so appearance has never bothered me.

Katie: No I personally don’t feel any added pressure other than to look after myself in terms of my health. I try to eat the right things and get enough sleep. I don’t think worrying about what your body looks like should be the biggest thing – it should be yourself and your health.

It’s common for social media to heap pressures on millennials. Will you stay active online during Wimbledon or will it be a hindrance?

Katie: I will definitely stay on there. It’s nice to take your mind off tennis during the Championships.

Aidan: Yeah of course. I think it’s quite fun during tournaments.

Are you ever worried about the negativity some people receive online?

Katie: No. Honestly it’s pretty funny when you read some of the messages. I would never take it to heart.

Who is your favourite account to follow on Instagram?

Aidan: Conor McGregor. I love his posts.

Katie: The Love Island account!

Aidan: Oh that’s embarrassing!

Follow Katie and Aidan’s progress through Wimbledon on BBC Sport online.