|Venue: Flushing Meadows, New York Dates: 29 August-11 September|
|Coverage: Live radio commentary on Radio 5 live sports extra plus live text coverage on the big matches on the BBC Sport website and app.|
World number one Novak Djokovic began his US Open campaign with victory over Poland's Jerzy Janowicz - despite the Serb requiring treatment to his arm.
Djokovic, who has struggled with a wrist injury, won 6-3 5-7 6-2 6-1 after calling the trainer in the first set.
Spanish fourth seed Rafael Nadal beat Uzbekistan's Denis Istomin 6-1 6-4 6-2.
Germany's Angelique Kerber, seeded second in the women's draw, led Polona Hercog 6-0 1-0 when the Slovenian succumbed to leg cramps.
I'm just glad to come through - Djokovic
Djokovic had spoken ahead of his opening match about the left wrist injury that has hampered him since the Olympics, but it was the right arm that appeared to be troubling the Serb against Janowicz.
He called a medical timeout after the fifth game to allow the trainer to work on his elbow and upper arm, but promptly broke the Janowicz serve on his way to the first set.
A wildly uneven display from both men saw Janowicz level at one set all after Djokovic double-faulted and blazed a forehand wide, shaking his right arm in apparent discomfort.
The defending champion began the second set serving at below 90mph but Janowicz was too inconsistent to take advantage, and Djokovic eventually ran out a comfortable winner - at least in terms of the scoreline.
He goes on to face Jiri Vesely in round two - the Czech who beat him in Monte Carlo earlier this year.
On calling for the medical timeout, the Serb said: "It was just prevention. It's all good. It's getting better and better each day.
"Hopefully as the tournament progresses, I'll reach my peak.
"There are periods when you're not feeling 100% but I don't think it's necessary to talk about this now. I'm just glad to come through this day and let's keep on moving."
There was an early shock in the men's draw as Britain's Kyle Edmund upset French 13th seed Richard Gasquet 6-2 6-2 6-3.
John Isner, the 20th seed, almost followed Gasquet out of the tournament but the American came back from two sets down to beat 18-year-old compatriot Frances Tiafoe 3-6 4-6 7-6 (7-5) 6-2 7-6 (7-3).
"It hurts, it hurts a lot," said Tiafoe, who served for the match in the fifth set. "Especially not getting over the line."
Nadal, who missed the French Open and Wimbledon with a wrist injury, said after his win: "The most important thing is that I am here in New York. Injuries are part of the career. I had a hard time this year."
Women's third seed Garbine Muguruza of Spain avoided an upset as she fought back to beat Belgian Elise Mertens 2-6 6-0 6-3.
Olympic champion Monica Puig was beaten in her first match since winning gold in Rio, going down 6-4 6-2 to China's Zheng Saisai.
Kerber resumes bid to be number one
Australian Open champion Kerber made it through to round two without dropping a game, as she looks to land a second major title and end Serena Williams' 185-week run at the top of the rankings.
Kerber, 28, came within one match win of toppling the American eight days ago in Cincinnati, and Muguruza and Agnieszka Radwanska also have a chance to do so in New York.
"To be one day number one, I think this is a goal from everybody, especially also for me," said Kerber.
"But I will not put too much pressure on myself because I know that when I put the pressure on, I'm not playing my tennis then."
Monfils takes time out
Gael Monfils overcame Luxembourg's Gilles Muller - and a close encounter with an on-court scoreboard - to progress to round two.
The Frenchman, seeded 10th, won 6-4 6-2 7-6 (7-5) to take his summer hard-court record to an impressive 15-2.
However, he almost came a cropper when he collided with a courtside clock on court 17, causing it to topple over and break.
"When you are in the moment you don't feel really anything," said Monfils. "Just jump. I saw a wall, but it was quite lucky."
Keys shows no signs of tiredness
American Madison Keys overcame compatriot Alison Riske in a closely-fought match to reach round two.
The match, which finished 4-6 7-6 6-2, is officially the latest finish to a women's singles match at the US Open having concluded at 01:49 local time.
Having won the first set, Riske was a break up in the second set tiebreak before eighth seed Keys began to take control.
"I looked up and it's almost 2am so who wants to go party," Keys told Eurosport.
"To be honest my party is going to be a protein shake and then sleep but everyone else can party for me."
Russell Fuller, BBC tennis correspondent:
"Djokovic voiced concern about the strength of his left wrist last week, but it was his right arm which needed on court treatment just five games into the defence of his title. He stretched out his arm at regular intervals, and looked in some discomfort.
"The world number one struggled at times with his serve and was frequently erratic, but still comfortably good enough to win a match against a man who has just returned from a six-month injury lay-off.
"He gave very little away in his post-match interview, preferring instead to look ahead and point out the importance of peaking at the end of the fortnight."