French world number 31 Alize Cornet was given a code violation for taking her shirt off on court during her US Open first-round defeat by Johanna Larsson.

Cornet changed her shirt during the break between the second and third sets, but realised it was back-to-front and quickly switched it on court.

But the chair umpire gave her a warning – despite male players being permitted to change their shirts on court.

Cornet lost 6-4 3-6 2-6 to Sweden’s Larsson in the searing New York heat.

On Tuesday, temperatures close to 38C (100F) at Flushing Meadows were made more stifling by humidity levels of over 50%, with five male players forced to retire due to heat-related issues.

The Women’s Tennis Association’s (WTA) rules state female players are not permitted to change their clothing on court, and instead must do it in a dressing room.

Male players regularly change their shirts on court at the change of ends.

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Conditions at the US Open were described as “dangerous” as five men had to retire from their first-round matches on Tuesday because of heat-related issues.

Temperatures close to 38C (100F) in New York were made more stifling by humidity levels of over 50%.

French player Julien Benneteau, who won on day two, said matches in the middle of the day should not have been played.

“They were lucky they only had retirements,” said the world number 60.

The conditions led to tournament organisers implementing an extreme heat policy in men’s matches for the first time.

Wimbledon champion Novak Djokovic, who said he “struggled” with the heat in his win over Marton Fucsovics, added that the physical issues affecting some players were “really sad to see”.

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Six players were forced to retire from matches on Tuesday, with the United States Tennis Association (USTA) saying five of the withdrawals – Italian qualifier Stefano Travaglia, Lithuanian Ricardas Berankis, Argentine Leonardo Mayer, Russia’s Mikhail Youzhny and Serb Filip Krajinovic – were “heat-related”.

For Youzhny it was a sad end to his final Grand Slam tournament, with the former world number eight set to retire from tennis next month at the age of 36.

The women’s WTA has an extreme heat policy for its players, unlike the men’s ATP, which has a discretionary rule.

USTA managing director Chris Widmaier said the decision to introduce it for the men was made after consulting its medical team.

The ruling offered a 10-minute break to both players after the third set and was taken if either or both wanted it.

The break took place in women’s matches between the second and third sets.

‘We were naked in ice baths’

Former world number one Djokovic and his Hungarian opponent Fucsovics were the first players to take a break after both suffered in the high temperatures.

The Serb revealed that they used the time to sit in cold baths together.

“Marton and I were in ice baths next to each other. We were naked in the ice baths and it was a quite wonderful feeling.”

“It wasn’t fun to play in the heat,” said Fucsovics, who lost in four sets. “I was dying after each point. It was too hot for tennis. It’s dangerous.”

Djokovic, who asked for a sick bucket to be put next to his chair in the second set, added: “There’s so much cramping going on. You don’t want to see that.

“You have to be fit, of course. I agree with that. But there are some conditions that are so extreme that, as fit as you are, you can’t just not feel it.”

The USTA said it would make a decision on Wednesday, when conditions are forecast to be similar, whether to implement the heat rule for a second time.

“We will be doing this on a case-by-case basis,” Widmaier added.

He said the show-court Arthur Ashe and Louis Armstrong Stadiums do not have air conditioning when the roofs are closed, although they may be shut overnight in an attempt to cool the courts.

Five-time Grand Slam champion Maria Sharapova held off a spirited fightback from Swiss veteran Patty Schnyder to reach the second round of the US Open.

The Russian defeated Schnyder – who, at 39, is the oldest player ever to make the main draw of a Grand Slam via qualifying – 6-2 7-6 (8-6).

The match was Schnyder’s first in a Grand Slam since she came back to tennis in 2015 having retired in 2011.

“I knew I was in for a battle no matter her story or my story,” said Sharapova.

“For her to come back and have the desire is really admirable. I’m just really happy I was able to win that last point.”

Sharapova, 31, will play Romanian Sorana Cirstea in the second round in New York.

• Konta knocked out in US Open first round
• Heat forces five retirements
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• Federer cruises into second round
• Djokovic wins after ‘struggling’ in heat

Schnyder, who reached the quarter-finals at Flushing Meadows in 1998 and 2008, said: “It actually doesn’t feel so special and it doesn’t feel like I’ve been gone for such a while. It has been part of my life for so long.”

In their first meeting in 10 years, world number 186 Schnyder was handed an early break by Sharapova – who was crowned US Open champion in 2006 – after the Russian made three double service faults in the opening game.

Serving did not improve on either side of the net with the first four games all breaks, before Sharapova held for the first time to take a 3-2 lead.

From there, the 22nd seed dictated the first set, taking it in 40 minutes, and looked to have eased through the second having built a 5-1 advantage.

But errors started to creep into Sharapova’s game allowing Schnyder to level at 5-5 before forcing the tie-break, in which Sharapova – who hit 23 winners but made 46 unforced errors – needed four match points to seal victory.

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Andy Murray will be hoping to prevent Fernando Verdasco from gaining the upper hand during Wednesday’s second-round encounter at the US Open.

The 31-year-old plays the Spanish 31st seed in the second match on Arthur Ashe Stadium at about 19:00 BST.

Murray beat James Duckworth on Monday in his first Grand Slam match in 14 months after hip surgery.

British number two Cameron Norrie faces Serb Dusan Lajovic in the third match on court 10 at approximately 20:00.

Murray said: “Fernando is a great shot-maker and someone, that when he’s on his game, is really tough to beat.”

Verdasco said: “I need to treat it like any other meeting, it won’t change just because he has been injured. Hopefully, Wednesday is going to be a good day for me.”

Murray, the 2012 US Open champion, has won 13 of his 14 meetings with Verdasco but had to come from two sets down to beat him in the 2013 Wimbledon quarter-finals.

• Djokovic wins after ‘struggling’ in heat
• Konta knocked out in US Open first round
• Wozniacki reaches US Open second round

Norrie wants bigger prizes for London home

Norrie, who beat Jordan Thompson in his opening match, has enjoyed a rapid rise up the rankings since turning professional in spring 2017 and is now up to 67 in the world.

To date, the 23-year-old has earned £522,000 in prize money, with at least an extra £42,000 from this year’s US Open.

Norrie, who is based at his former college in Texas, USA, is hoping use his prize money to buy a London flat.

He joked of the property prices: “I’ll probably have to make the semis here. Maybe [I’ll need to] win it for Putney or Wimbledon.”

Serena Williams and Nadal headline night session

As they did on Monday, defending men’s champion Rafael Nadal and six-time women’s champion Serena Williams feature in the night session on Arthur Ashe Stadium.

American Williams, seeded 17th, faces German Carina Witthoeft at 00:00 and will be followed by Nadal’s match against Canadian Vasek Pospisil.

Defending women’s champion Sloane Stephens opens proceedings on the main court at 16:00 against Ukraine’s Anhelina Kalinina, with Murray straight after.

Women’s seventh seed Elina Svitolina, two-time champion Venus Williams and men’s third seed Juan Martin del Potro are all in action on the Louis Armstrong Stadium.

If both Williams sisters win, they will meet in the third round.