|Venue: Flushing Meadows, New York Dates: 31 August-13 September|
|Coverage: Live radio and text commentary on every Andy Murray match plus selected matches.|
Second seed Roger Federer made smooth progress on another hot day at the US Open that brought more retirements.
The five-time champion, 34, beat Belgian Steve Darcis 6-1 6-2 6-1 to reach round three.
Stan Wawrinka, Simona Halep and Petra Kvitova were among the other winners as the temperature and humidity rose.
In temperatures reaching 33C, Jack Sock and Denis Istomin took the tournament total to 14 retirements - equalling the Grand Slam record after two rounds.
Federer, 34, needed just one hour and 20 minutes to see off Darcis and set up a meeting with Germany's 29th seed Philipp Kohlschreiber.
The Swiss star's victory against the world number 66 in Thursday's night session equalled Serena Williams' record for most US Open wins under the lights in Arthur Ashe Stadium.
"I've enjoyed myself so many times, so many years. It's wonderful that I can still experience it and play this well," said 17-time Grand Slam winner Federer. "I hope this is not my last one, of course."
In the final match of the day, Czech world number 149 Petra Cetkovska saved four match points to upset Danish fourth seed Caroline Wozniacki 6-4 5-7 7-6 (7-1).
Sock retires after fainting on court
American Sock had to be carried off court after fainting and then retiring from his match against Ruben Bemelmans.
The 28th seed won the first two sets but, with temperatures rising and humidity at 50%, needed treatment after the Belgian won the third.
Sock started cramping as he trailed 2-1 in the fourth set and needed a trainer to help him sit down on the court.
The 22-year-old was treated with ice packs and cold towels and, after a wheelchair was brought onto court, managed to limp off with the help of medical staff.
''Playing in the US Open is the biggest and most important moment of the season for me," Sock later said in a statement.
"Having to retire from my match today is extremely disappointing. I want to thank everyone for their support and can't wait to be back next year. I feel better already and look forward to playing Davis Cup."
A few hours after Sock's retirement, Uzbekistan's Istomin, 28, also pulled out of his match against Dominic Thiem on court seven. The Austrian 20th seed was leading 6-4 6-4 1-0.
Hewitt bows out to Tomic
It was almost the perfect comeback in his final US Open, but Lleyton Hewitt fell just short against fellow Aussie Bernie Tomic.
"It was really awkward," said Hewitt, who will retire from tennis after the 2016 Australian Open. "I get along well with Bernie, he's a good guy and moving along in the right direction."
The 34-year-old, who won the title in 2001, thrilled the Grandstand crowd as he came from two sets down to earn two match points, and then served for the match.
It was not to be, however, as 22-year-old Tomic reeled off the last four games to win 6-3 6-2 3-6 5-7 7-5.
"He was in that mood of going for everything and a couple of shots went in," Hewitt said of the match points.
Who else is through?
French Open champion Stan Wawrinka will meet Bemelmans in the next round after needing over three hours to beat South Korean teenager Chung Hyeon 7-6 (7-2) 7-6 (7-4) 7-6 (8-6).
In the women's singles, second seed Simona Halep eased past qualifier Kateryna Bondarenko in a 6-3 6-4 win. The Romanian, 23, has dropped just nine games in her opening two victories.
After success for Jamie Murray and Dom Inglot on Wednesday, three more Britons made progress in the doubles on Thursday.
Scotland's Colin Fleming and Treat Huey of the Philippines beat fifth-seeded Italians Simone Bolelli and Fabio Fognini 6-1 6-7 (3-7) 7-6 (8-6).
England's Jonny Marray and New Zealander Marcus Daniell beat American wild cards Reilly Opelka and Taylor Harry Fritz 6-3 4-6 6-3.
And Laura Robson teamed up with Belgian Kirsten Flipkens to beat Americans Madison Keys and Lisa Raymond 6-2 6-4.
Drone strike on Armstrong
There was an unusual interruption to the match between Flavia Pennetta and Monica Nicolescu on a sparsely attended Louis Armstrong Stadium.
A remote-control drone crashed into the seating, causing play to be halted as police officers examined the unexpected intruder.
"I feared the drone was a bomb," Pennetta told tennisworlditalia.com. "With all the news out there, I thought it was over. My team was so scared."
"No spectators were in the immediate area of the crash and there were no injuries. The New York Police Department responded and is conducting an ongoing investigation," said a US Open statement.
Quotes of the day
"It's difficult with sweating buckets. I mean, after changing the clothes they literally weighed like a lot." Britain's Jo Konta was not immune to the conditions despite her win.
"I warmed up at 11:30 and it was pretty toasty during the warm-up. I had a good time today." American 13th seed John Isner, who beat Mikhail Youzhny in straight sets, was another to succeed in the heat.
"When you are still in the tournament, you try and book a car, they say you can't have one before 10am because you don't have a match - I don't think it's good enough." Former champion Sam Stosur is one of many to have issues getting to Flushing Meadows.
"Because I prefer bus." In more transport news, second seed Simona Halep is asked why she did not get a car to the site.