By Simon Evans
MASON, Ohio (Reuters) - Andy Roddick needed three sets to beat 46th-ranked Ukrainian Sergiy Stakhovsky 6-4 6-7 6-1, while fellow American Taylor Dent upset Feliciano Lopez to advance to the second round of the Cincinnati Masters on Monday.
Roddick, who has struggled for form and fitness in recent weeks and said he had been suffering from the 'mono' virus, produced some powerful serves but had to stay alert against an opponent playing some enterprising if erratic tennis.
The Ukrainian came out on top in the tiebreak at the end of a tight second set, leaving Roddick to throw his racket to the floor in frustration.
The American, however, broke early in the third to take a firm grip on the match and never looked back.
"It was almost a blessing in disguise that I got to play the third set, because that's the best I've played in a couple months," said Roddick, who was also pleased to cope with the physical demands of a three-setter lasting two hours, 15 minutes.
"I lost the second set, but I came right back and I was able to get back on top. So I thought I did a good job of that."
Dent, who last won an ATP tournament in 2003, beat Spaniard Lopez 6-3 6-2 in perfect conditions on center court to set up a second-round clash with world number one Rafa Nadal.
Dent, ranked 83rd, does not expect to get much in the way of home support given Nadal's popularity and said his only hope was to get on top early against the Spaniard.
"Dictate play consistently ... best scenario, I go out on the court and I'm hitting a lot of first serves in, hitting a lot of big second serves in, and taking those first and second balls and really not giving him a chance to set up and hit forehands," he said.
"Worst case scenario, he's setting up and hitting forehands. I would rather hit errors than have him just wind up all day on that forehand. I think he's probably got the best forehand in the game right now.
Switzerland's Stanislas Wawrinka comfortably defeated Spaniard Nicolas Almagro 6-3 6-3 and will play the winner of the all-French match between Michael Llodra and Julien Benneteau.
Sam Querrey completed a good day for the United States by beating German Philipp Petzschner 6-1 6-4.
The top four seeds -- Nadal, Roger Federer, Andy Murray and Novak Djokovic start their action Wednesday.
(Editing by Ian Ransom and Peter Rutherford)