Novak Djokovic made a scratchy start while Andy Murray motored through as the pair of seeds won opening matches after byes on Wednesday at the ATP-WTA Cincinnati Masters.
Djokovic, seeded second behind Roger Federer, did not even have the chance to hit on the showcase court after arriving in the Midwest from his post-Olympic title in Toronto at the weekend. But the Serb toughed out a defeat of Italian Andreas Seppi 7-6 (7/4), 6-2.
Murray, the Olympic gold medallist who played one match last week in Toronto and then quit with a sore knee, showed no sign of injury as he efficiently handled American Sam Querrey 6-2, 6-4, taking just 83 minutes to get his game into shape.
Djokovic was not impressed with his own form, calling his win "not a great performance."
The winner of three grand slams in 2011 improved to 9-0 over Seppi, whom he struggled with at Roland Garros in a comeback from two sets to love down in the fourth round.
"I didn't do anything special out there. I was just trying to get used to conditions, trying to keep the ball on the court and hit one more than my opponent.
"This happens in every first match, you have to get used to quite different conditions. I came in late from Canada and it feels a lot different here."
Djokovic won in just under 90 minutes, a contest which included a 59-minute opening set in which the second seed needed four set points to take the lead.
The Serb stepped it up in the second. He had 21 winners and 22 unforced errors.
Djokovic will line up in the third round against Russian veteran Nikolay Davydenko, who beat Florian Mayer of Germany 6-3, 6-3.
Top seed and four-time champion Federer was opening later against Alex Bogomolov.
Argentine sixth seed and former US Open winner Juan Martin del Potro knocked out Germany's Tommy Haas 7-5, 6-2, But Czech Radek Stepanek returned the favour with his defeat of Argentina's eighth seed Juan Monaco 7-6 (7/2), 6-1.
Mardy Fish, the US tenth seed, beat Argentine Carlos Berlocq 6-3, 6-1.
Croatian 12th seed Marin Cilic put out Jesse Levine 7-5, 7-6 (8/6) and Australian wild card Lleyton Hewitt went down to Serb Viktor Troicki 6-2, 6-0 after not getting to bed until 3 a.m. in his Monday late-night opening win.
In the women's second round, top seed Agnieszka Radwanska dispatched Swede Sofia Arvidsson 6-4, 6-3, with number four seed Petra Kvitova came back to knock out German Mona Barthel 3-6, 6-2, 7-5.
Italy's seventh seed and Roland Garros finalist Sara Errani beat Slovak Daniela Hantuchova 6-4, 6-4.
"The first match is always the most difficult, every week we play on different surface and different balls and different conditions," said 2011 Wimbledon winner Kvitova.
"I'm just happy that I went through, especially in two sets, because today was really, really hot. I'm hoping I can play better tennis tomorrow."
Slovak 11th seed Dominika Cibulkova was unable to finish as she retired in her match against Andrea Hlavackova, losing 7-6 (7-1), 4-1.