British number one Andy Murray had to come from a set down to defeat Korea's Hyung-Taik Lee and reach the last four at the Sap Open in San Jose.
Murray faces a repeat of last year's semi in which he beat Andy Roddick
Murray, the reigning champion at the Californian event, struggled for form early on and lost the first set 6-4.
He took the second set after an early break and then served for the match after breaking at 5-5 in the decider.
But Lee saved a match point and hit back to force a tie-break before Murray prevailed 4-6 6-3 7-6 (7-4).
The Scot will now face top seed Andy Roddick in the semis, after the American beat Vince Spadea in three sets.
Murray said: "I thought I did well to get through. It's great for my game to be playing these kind of players (like Roddick).
Andy makes you beat him. He is a very, very good player
Andy Roddick is wary of next opponent Murray
"The most important thing is to return well and to try to take care of my serve."
Eighth seed Spadea hit back from a break down in the second set to force a decider but Roddick, recovered to win 6-3 6-7 (5-7) 6-1.
Roddick said: "My focus was all over the place in the first two sets.
"I don't know why, but then the third set was probably the best set I have played all week."
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The American was beaten in straight sets by Murray last year and also lost to him at Wimbledon, though he did gain some revenge by beating the Scot in Cincinnati in August.
"Andy makes you beat him," Roddick said. "He can go for the ball big and he plays great defence. He is a very, very good player."
Germany's Benjamin Becker upset Marat Safin 6-4 6-3, and will take on unseeded Croat Ivo Karlovic, who overpowered American Mardy Fish 7-6 (7-2) 6-4.
"I think I played pretty well and I think he made a few more mistakes than he usually does," Becker said after beating Safin.
"I just tried to him play a lot, not going for too much, especially on his serve and it worked out."
Karlovic was delighted with his progress after missing much of last year through injury.
"I didn't expect to do this well, so I am very happy, I'm playing better and serving better."
Fish agreed that Karlovic's serve was the key to the match.
"It's basically a crap-shoot when you play him," Fish said. "It doesn't really feel like tennis.
"It's not often you play a match where you are excited to reach 40-30. He serves so well and you just don't know where it's going."