Olympic champion Andy Murray battled into the second round of the US Open on Monday while defending women's champion Samantha Stosur and third seed Maria Sharapova cruised in their opening matches.
And three-time US Open champion Kim Clijsters stretched her win streak on the Flushing Meadows hardcourts to 22 matches while world number ones Roger Federer and Victoria Azarenka were scheduled for later night matches.
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.
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 while Russia's Sharapova dispatched Hungary's Melinda Czink 6-2, 6-2.
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.
"It was great to get out there again," Stosur said. "I felt like I was ready to go. It was a good start. I certainly won't complain about being out there. I'm really happy with the way I played."
Sharapova, who completed a career Grand Slam by winning the French Open last June for her fourth major, had not played since losing to Serena Williams in the Olympic final but looked solid, advancing in only 67 minutes.
"I was just happy to be back on the court," Sharapova said. "I haven't had a match in a few weeks."
Belgium's Clijsters, playing in the final event of her career at age 29 so she can spend more time with her family, defeated US teen Victoria Duval 6-3, 6-1, on the same court where she won US Open crowns in 2005, 2009 and 2010 and hopes to claim another in her final bow.
"I've always felt very comfortable as soon as I step on the hardcourts and in New York," Clijsters said.
"There's a lot of positive emotions I use when I'm out here. I've had some good practices and I'm trying to carry that into the matches."
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.
"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."
Next up for Murray will be Croatia's Ivan Dodig, who dispatched Japanese qualifier Hiroki Moriya 6-0, 6-1, 6-2.
Stosur won the first 19 points of her match before a double fault ended her bid for a golden first set.
"It was 19 points in a row. You knew you were going to lose one at some point," Stosur said.
"I knew at 4-0, 40-0 that I hadn't missed a point and the match had been going pretty quick. It did pop into my head for a split second. Then I hit the double fault and it was erased."
The 28-year-old from Brisbane will next face Romanian qualifier 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 matchup against Aussie Casey Dellacqua, who ousted Ukrainian qualifier Lesia Tsurenko 6-2, 6-3.
"Maybe this year, I just was in the final Montreal and I won in Cincy, so I got a lot more confident," Li said.
Czech fifth seed Petra Kvitova advanced 7-6 (8/6), 6-1 over Slovenia's Polona Hercog.