Two-time champion Novak Djokovic moved into the US Open third round after needing four sets to beat big-hitting American Tennys Sandgren.

Djokovic, 31, missed a match point in the third set before Sandgren dominated the tie-break.

But the Serb broke twice in the fourth set to win 6-1 6-3 6-7 (2-7) 6-2.

The sixth seed, chasing a 14th Grand Slam title, will play France’s Richard Gasquet or fellow Serb Laslo Djere next.

“I thought I played very well for the first two sets, two sets and a half, and then lost it mentally, said Djokovic, who praised Sandgren for his fight.

“I’m not happy with the way I lost concentration and composure but I managed to regroup in the fourth.”

Djokovic not at best but avoids major drama

Djokovic survived a slight scare in his opening match after needing “survival mode” in sweltering conditions on Tuesday lunchtime to battle past Hungarian opponent Marton Fucsovics.

In lower heat and humidity in Thursday’s night session on Arthur Ashe Stadium, there was no major drama for Djokovic – despite 27-year-old Sandgren making the former world number one stay out on court longer than he would have liked.

Sandgren, ranked 61st, won just six games when the pair met at Wimbledon in July and looked set for a similar pummelling.

Djokovic edged the key points in a first set which he won in 32 minutes, then was untroubled on his serve in the second set before breaking Sandgren twice to win the final four games.

But Sandgren, backed by a supportive home crowd under the floodlights, started finding his range in a third set where he hit 16 winners.

He saved a match point at 5-4 with a forehand down the line and served out again to force the tie-break.

Sandgren’s power blew Djokovic out of the breaker, but he ran out of steam as Djokovic wrapped up the fourth set in 33 minutes.

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Elsewhere, seventh seed and 2014 champion Marin Cilic raced through a 6-2 6-0 6-0 win over Poland’s Hubert Hurkacz in just one hour 19 minutes.

World number four Alexander Zverev advanced to the third round for the first time with a comprehensive win over France’s Nicolas Mahut.

The 21-year-old German won 6-4 6-4 6-2.

Fourteenth seed Fabio Fognini fell victim to Australian John Millman, losing 6-1 4-6 6-4 6-1.

Kei Nishikori progressed to the third round when Frenchman Gael Monfils retired injured in their match with the Japanese 21st seed leading 6-2 5-4.

Monfils was hurt when a volley hit his right wrist.

Australian world number 30 Nick Kyrgios fought back to beat Pierre-Hughes Herbert at the US Open after an apparent pep talk from the umpire.

Kyrgios was a set and 0-3 down to his French opponent when official Mohamed Lahyani climbed down from his chair during a changeover.

“I want to help you. This isn’t you. I know that,” Lahyani said.

Krygios went on to win 4-6 7-6 (8-6) 6-3 6-0 and could play world number two Roger Federer next.

Swiss Federer, a five-time champion at Flushing Meadows, is playing France’s Benoit Paire for a place in the last 32.

Kyrgios claimed after the match that Lahyani was concerned about his medical well-being rather than his motivation in their on-court discussion.

“He was just concerned about how I was playing – he was like: ‘Nick are you OK?'” said Kyrgios.

“I was like: ‘Yeah everything is fine.’ I just wasn’t feeling great.”

The 23-year-old won 19 of 25 games after the exchange and the incident sparked debate online.

Kyrgios, who hit 25 aces in his first-round win over Radu Albot, delivered the joint-fastest serve of the tournament so far with one 142mph tee-off.

Elsewhere world number four Alexander Zverev advanced to the third round for the first time with a comprehensive win over France’s Nicolas Mahut.

The 21-year-old German won 6-4 6-4 6-2.

Fourteenth seed Fabio Fognini fell victim to Australian John Millman, losing 6-1 4-6 6-4 6-1.

Andy Murray joked he need a check-up as he has “started imagining things” after Fernando Verdasco denied he had spoken to his coach during the heat break in their US Open second-round tie.

Players are not allowed to be coached during breaks for extreme heat.

Murray reported Verdasco, who won in four sets, but the Spaniard said: “I don’t want to say that Andy lied but I didn’t talk one word with my coach.”

Murray later posted a response using the hashtag #liarliarpantsonfire.

Writing on Instagram, Murray thanked fans for their support and joked: “I’m off to get a health check as apparently I’ve started imagining things.”

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Earlier, following his 7-5 2-6 6-4 6-4 defeat, Murray had said Verdasco and his coaching team “probably weren’t aware of the rule” about heat breaks.

“When I came out of the shower, his coach and one of the Spanish doubles players were in there chatting to him, and you’re not allowed to speak to your coach,” said Murray.

“I’m not blaming Fernando and his team. They certainly weren’t trying to break any rules.

“It shouldn’t be for the player that’s competing against him to have to go to the supervisor.”

Both players left the Arthur Ashe court at the end of the third set after Spaniard Verdasco took up the 10-minute extreme heat break with temperatures rising close to 100F (38C).

However, the 34-year-old denied Murray’s claim, saying his coach was only in the locker room to go to the toilet.

“I was in the ice bath with Marcos Baghdatis and his coach,” Verdasco said.

“I know exactly the rule and I don’t want to be the one breaking it.”

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Andy Murray says it is “completely normal” to have doubts about whether he can return to the top of the game after his Grand Slam return ended in a second-round defeat at the US Open.

The British former world number one lost in four sets to Spanish 31st seed Fernando Verdasco at Flushing Meadows.

Murray, 31, was playing best-of-five matches for the first time since hip surgery in January.

“You just don’t know exactly what’s round the corner,” he said.

Murray, a three-time Grand Slam champion, has only played five tournaments since returning to the ATP Tour in June after an 11-month absence with the hip problem.

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Now ranked 382nd in the world, Murray said he played some of the best tennis of his comeback against Verdasco, but also lamented making mistakes and admitted it “wasn’t the most comfortable” he had felt on court.

“When I got the injury, I was ranked number one in the world, 12 months later things completely changed,” he said.

“If things keep going smoothly, physically I continue to improve, I believe that I will get back to competing for the biggest competitions because there’s no reason why I couldn’t.

“When you continue to build up and start playing more tournaments, you don’t know how you’re going to respond.

“Because of the path that I’ve been on the last year with the many ups and downs, trying to come back, it not quite working, then ending up having the surgery, I think it’s completely normal to have those doubts.”

Murray eyes Davis Cup return

Murray says he would “love” to play in Great Britain’s Davis Cup tie against Uzbekistan in Glasgow next month.

But the Scot says he needs time to assess his fitness after his US Open exit.

“Potentially it’s the last time I’d get to play competitive tennis in Scotland so I’d like to do that,” he said.

“I’d have to chat to my team because this is obviously a very important period in my rehab and my long-term strategy.”

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Murray has long carried the flag for British tennis and helped his nation win the Davis Cup for the first time in 79 years when they beat Belgium in 2015.

He has not played in the competition since Britain suffered a semi-final defeat by Argentina in September 2016, missing three matches since through a combination of fatigue and injuries.

After returning to competitive action in June, he pulled out of Wimbledon before making his Slam return at Flushing Meadows on Monday.

An opening win against Australia’s James Duckworth was followed by defeat against Verdasco on Wednesday.

“Playing five sets takes a lot out of you, which I’ve obviously learned in the last couple of days, and the Davis Cup has also taken a lot out of me,” he said.

“But there’s a big part of me that would love to play and get the opportunity to play one last time in Glasgow.”

The controversial revamp of the Davis Cup, which comes into effect in 2019, means there will only be one home or away tie each year before a season-ending final held in a neutral venue.