Memphis - Top-seeded John Isner beat fellow American Donald Young 7-6 (3), 6-4 on Thursday to move to the quarter-finals of Regions Morgan Keegan Championships.
Isner, ranked 14th in the world, used his trademark big serve - with 22 aces - to dispatch Young in 1 hour, 43 minutes. They were on serve in the second set, when Isner broke Young for the match, with Young netting a forehand on match point.
Isner's quarter-final opponent will be Austrian Jurgen Melzer, who fought back to win a tight match against Croatian Ivan Dodig 2-6, 6-3, 7-6 (5).
Third-seeded Radek Stepanek progressed in another tight one, edging young American Ryan Sweeting 4-6, 6-3, 7-6 (4). The Czech will next meet another American in Sam Querrey, who eliminated seventh-seeded Kevin Anderson of South Africa 7-6 (4), 6-4.
Defending champion Milos Raonic of Canada also reached the last eight with a 6-4, 6-4 win over Ukraine's Sergiy Stakhovsky. His next opponent will be Belgian Olivier Rochus, who defeated American Ryan Harrison 6-4, 7-5.
The other quarter-final will be between Poland's Lukasz Kubot and German Benjamin Becker. Kubot was a 7-6 (5), 6-2 winner over German Philipp Petzchner while Becker downed Belgian veteran Xavier Malisse 7-6 (4), 6-4.
Young looked poised to beat Isner when he broke in the first set for a 4-2 lead. But Isner broke back immediately.
"When I was up that break in the first set, it would have been nice to have held in the next game to see what happened," Young said, later adding: "There were only a few missed points, but at this level, it's only going to be a couple of points that are going to be the difference."
Isner said he struggled early and was lucky to reach a tiebreaker in the first set.
"I didn't feel like myself from the get go," Isner said. "My feet were all over the place, I was out of position on every shot, and my forehand, which I rely on a lot, was pretty much missing."
Isner is undefeated in eight tiebreakers this year, including two in his first-round win over Gilles Muller of Luxembourg. Isner plays an unusually high number of tiebreakers because his serve is so hard to break, while he does not have his major weapon when receiving.
"That's usually when my adrenaline gets going the most," Isner said. "To have my serve as a weapon, it helps a lot in tiebreakers. I'm able to get cheap points. We're playing first to seven, so if I'm able to get to get two cheap points on my serve it puts so much pressure on my opponents. I find myself serving my best in the tiebreaker. I'm very comfortable, but I prefer not to play in them."
In the Memphis International, the women's side of the tournament, fourth-seeded Marina Erakovic of New Zealand was taken to three set before defeating Michaella Krajicek of the Netherlands 6-4, 6-7 (2), 6-4 in their quarter-final.
Erakovic - the only seeded player remaining in the field - will meet Vera Dushevina in the semi-finals. Dushevina beat Stephanie Foretz-Gacon 3-6, 6-3, 6-1.
Sofia Arvidsson also reached the semi-finals with a 6-2, 7-6 (9) win over Ukraine's Lesia Tsurenko and will take on Italian Alberta Brianti, who beat American Varvara Lepchenko 7-5, 6-3.