France's Gael Monfils won an error-filled match over Spaniard Fernando Verdasco 6-7 (8/10), 6-4, 6-4 on Thursday to edge into the semi-finals of the ATP Winston-Salem Open.
The 15th seeded Monfils will Friday face off for a place in the final when he takes on Ukranian tenth seed Alexandr Dolgopolov, who beat Lu Yen-hsun of Taiwan 7-6 (7/2), 6-3.
Monfils and seventh seeded Verdasco seemed to play their third match as if neither wanted to win in the closing stages.
The Frenchman, who is back this week after an ankle injury which forced him to miss the two Masters 1000 events this month, could not take advantage of many of the mistakes by Verdasco, whose unforced error count totalled well over 60 in the contest which lasted just under two and a quarter hours.
He hadn't played since reaching the Umag claycourt final in July.
"I lost two weeks of training because I sprained my ankle," Monfils said.
"This week means a lot to me. I was playing well before the ankle and had done well on clay in Europe. I was doing well when I got hurt.
"It's good to be winning matches to finally get set for the US Open," added Monfils, who has returned to the top 50 in the world after falling as low as 108th on February 2.
Monfils improved to 3-0 over Verdasco in the match-up between the pair of former top 10 players in the final tune-up event before the US Open, which begins Monday.
Verdasco failed to impress in his first hardcourt quarter-final of the season. Of his five previous 2013 quarter-finals, two came on grass and three on clay.
The Spaniard, who suffered a neck injury earlier in the year, produced 11 aces but had a dozen double-faults in a patchy performance in draining and humid conditions. At times it looked as both were struggling for energy.
Verdasco produced almost half of his errors in a first set which lasted nearly an hour. But he won it after saving Monfils set points and going through on his own second opportunity.
Monfils won the second set and came from 3-1 down in the third to finally advance as his seventh ace set up a match point. He clinched it when Verdasco hit a forehand long over the baseline.
World number 43 Monfils won his only other match with Dolgopolov in the first round of the Australian Open in January.
Dolgopolov dealt Lu his ninth career quarter-final defeat without a win as he advanced into the last four in one hour, 38 minutes. The Ukranian owns the series 3-0 including a win here last year.
In other quarter-finals, American sixth seed Sam Querrey faced Lithuanian Ricardas Berankis while Austria's Jurgen Melzer, seeded ninth, took on Russian Dmitry Tursunov.