When Sofia Kenin was closing in on her maiden Grand Slam title, her dad could barely watch.

Alex Kenin’s face was contorted with tension and then covered with his hands as he hunched forward nervously on his seat.

This was the moment they had dreamed of ever since she picked up a racquet aged five and became a child prodigy who hit with the stars.

When Kenin’s 4-6 6-2 6-2 win over Garbine Muguruza in the Australian Open final was complete, the 21-year-old American raced around the net to the opposite corner of the court to tenderly grasp the hand of her father, who is also her coach.

She says they both asked each other what had just happened.

Two hours or so later, with the Daphne Akhurst trophy on the table and a glass of Champagne in her hand, she had a simple message to the man who gave her the “American dream”.

“Just thank you to him. We can share this forever,” said Kenin.

Alex, a quiet Russian who moved to New York in 1987, responded by using his two index fingers to draw a smile on his face.

“He saw I had talent and we said ‘let’s just go for it and do this professionally for my life’,” said Kenin, who will rise to seventh in the world when the rankings are updated on Monday.

“He knows what he is talking about and comes up with the right plans and the right strategies. He just knows it.

“He did it by learning the whole experience. He is crazy smart.”

What makes Kenin’s rise remarkable is the fact her dad has guided her all the way there as a self-taught coach with little background in the sport.

Alex drove one of New York City’s iconic yellow cabs before becoming a computer consultant, then took over as her coach when his daughter’s career became more serious.

He played tennis “just for fun” in his younger days back home in Moscow and Crimea but says he did not play “well”.

It was apparent his daughter, who Alex and wife Svetlana took to be born back in Russia before returning to Manhattan shortly afterwards, was a special talent.

She quickly became a star in the States, featuring on television programmes and the covers of magazines which labelled her as a future Grand Slam champion.

Famously, aged seven, she claimed she would be able to return a serve from hard-hitting American star Andy Roddick, then practised with the likes of Grand Slam champions John McEnroe, Venus Williams and Kim Clijsters.

The WTA posted a video this week of four-time Grand Slam singles champion Clijsters giving a tour to a then six-year-old Kenin, with the Belgian saying “who knows, she might be one of the new big stars”.

Quickly she rose through the junior ranks, with two-time Grand Slam champion Naomi Osaka even saying recently that Kenin “killed it” during those years.

The constant by her side has been her dad, who says he was never tempted to hire a ‘professional’ coach.

“She was always number one at 12, 14, 16, 18. So why change a good thing?” said Alex, who thanked journalists for their “attention” after he spoke to them.

His daughter has become the youngest Australian Open champion since Maria Sharapova in 2008 and the eighth woman to become a first-time Grand Slam winner in the past 12 events.

As with Japanese 22-year-old Osaka and 19-year-old Canadian Bianca Andreescu before her, she has become the latest young star to leave the world wondering if she can go on to dominate the game.

Throw American 15-year-old Coco Gauff, who Kenin impressively beat in the last 16 in Melbourne, into the mix and the future of the women’s game looks bright.

“I saw what Naomi and Bianca achieved and I really wanted to achieve that,” said Kenin, whose given name is Sofia but is known by its diminutive Sonya – the name of Alex’s mother – at home.

“It gave me a big boost, big motivation.

“My dad was telling me: ‘It is great for them and you can really achieve this too’.

“I’ve seen women’s tennis is changing. We can all play each other on any given day and there can be a lot of damage happening.”

Muguruza, a two-time Grand Slam champion, can testify as to the damage Kenin can cause.

The American’s relentless returning, ability to execute under pressure and an insatiable will-to-win ground down the Spaniard, who led by a set before being mentally and physically worn down in Saturday’s final in Melbourne.

Kenin swung the match her way with a monumental hold from 3-2 40-0 down in the third set.

Two backhands down the line under the most intense of pressure were outrageous, a third winner – this time down the other flank – almost ridiculous.

An ace out wide and a crosscourt forehand winner – after drawing Muguruza into the net – clinched the hold. It also virtually clinched the championship.

Muguruza crumbled from that point, producing three double faults – including one on match point – in what proved to be the final game.

“I knew I needed to come up with the five best shots of my life. I mean, let’s go!” laughed Kenin, who plans to spend some of her £2.1m winnings in luxury jewellery stores in Melbourne.

Growing up in the affluent Manhattan neighbourhood of Upper East Side, she says she is a “typical blonde girl” from that area.

“I’m into all those fancy stores,” said Kenin, who has almost doubled her previous career winnings of £2.9m.

“I like to have that luxurious life. I’ve worked so hard for it. it’s super exciting and I get to do what I want.”

That she is able to do that is down to father Alex and mother Svetlana, who was back home in Florida with Kenin’s grandma, sister and dogs.

Kenin said her mum cannot watch her matches because she gets too nervous.

“I called her right after the match just to tell her that everything’s fine, I won, she can just relax now,” said Kenin, who mouthed “Oh my God! Look at all these people” when she walked into a packed media room.

“I told her I’m not going to be able to talk to you for hours, but at least you know that I won.

“I’m coming home, you can give me the biggest hug of your life.”

Although the rest of the Kenin family could see exactly what was happening on Rod Laver Arena through the television pictures, Alex melted the hearts of more than a few people who watched him film his daughter’s maiden Grand Slam acceptance speech on his mobile phone.

Afterwards, sitting alone in a quiet media area and going through countless messages on the same device, he had a confession to make.

“It didn’t go too well, I didn’t press record properly,” he laughed.

It was probably the only mistake he has made this fortnight.

• Kenin wins maiden Grand Slam
• Kenin v Muguruza – as it happened
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