London Olympic champion Andy Murray laboured into the second round of the US Open while defending women's champion Samantha Stosur cruised in her opening match at the year's final grand slam showdown.
Britain's third-seeded Murray, still seeking his first grand slam title, struggled at times in dispatching Russia's 73rd-ranked Alex Bogomolov 6-2 6-4 6-1 after waiting out a rain delay of more than two hours at Flushing Meadows.
Murray put a scare into his supporters by clutching his left leg after a point in the fifth game of the final set but blamed the problem on cramping after being pushed throughout the match, which lasted two hours and 15 minutes.
"Struggling a little bit," Murray said. "There were a lot of long points, especially at the beginning of the match.
"Just a little bit of cramping. I have to stay better hydrated for the next matches."
Australian seventh-seed Stosur began her repeat bid with a 6-1 6-1 victory over Croatia's Petra Martic before showers drenched the New York hardcourts.
Stosur, seeking her first title since upsetting Serena Williams in last year's US Open final, fired 10 aces to advance in 51 minutes on the same Ashe Stadium court where she hoisted the trophy a year ago.
World number ones Roger Federer and Victoria Azarenka were scheduled for later matches with former US Open champions Maria Sharapova and Kim Clijsters also scheduled for action at the 23,700-seat main stadium.
Bogomolov, who changed his citizenship from American to Russian late last year, beat Murray last year at Miami in their first meeting and battled him at the start this time, the match opening with four breaks of serve.
Murray denied Bogomolov on two break points in the fifth game and held, then broke the Russian twice more, the first on a backhand volley winner and the last on a forehand winner to claim the first set after 43 minutes despite connecting on only 28 per cent of his first serves in the set.
"Both of us struggled early on," Murray said. "A six or seven out of 10. I didn't serve well at the beginning but I won in three sets against a tough player."
Bogomolov broke Murray to open the second set, the Scotsman squandering the point when a backhand off the net cord fell wide, and grabbed two break points in the fifth game before Murray battled back to hold.
But Murray broke back to 4-4 when Bogomolov sent a forehand long and broke again on a powerful forehand winner to claim the second set after 93 minutes.
Murray fired a backhand service return winner to break the Russian for a 2-0 lead in the third set, handed back the break by netting a forehand in the next game, but broke again for a 3-1 edge and held to the finish.
Next up for Murray will be either Croatia's Ivan Dodig or Japanese qualifier Hiroki Moriya.
Stosur will face a qualifier in round two - either Swiss Stefanie Voegele or Romania's Edina Gallovits-Hall.
Chinese ninth seed Li Na, a first-round US Open loser the past two years, beat Britain's Heather Watson 6-2 6-3 to book a second-round match-up against Aussie Casey Dellacqua, who ousted Ukrainian qualifier Lesia Tsurenko 6-2 6-3.
"I'm really happy I won the first match. Last few years I always lose first round," Li said. "You really have to win the first match, otherwise same like last year and I have to pack, I have to go back to airport to fly back home.
"Maybe this year, I just was in the final Montreal and I won in Cincy, so I got a lot more confident."