Andy Roddick rifled over his ninth ace to set up a match point and finished off a 6-1, 6-4 defeat of Juan Monaco Thursday as the American continued to lift his game at the ATP Winston-Salem Open. Top seed Roddick is making up for a lost summer, the majority of which he sat out with a post-Wimbledon abdominal muscle strain. The former number one and 2003 US Open champion will play for his first final since February in Memphis when he faces compatriot John Isner on Friday. Fourth seed Isner reached the semi-finals for the fourth time in his last six events with a 1-6, 6-3, 6-4 victory over Cyprus's Marcos Baghdatis, the player he'll meet in the US Open first round next week. The North Carolina event, which is likely to avoid the full force of Hurricane Irene, was the setting for wild card and 21st-ranked Roddick to show off the tennis which made him a regular in the top 10 for a decade, until his slide in 2010. The American overwhelmed Argentina's Monaco, with Roddick sweeping the opening set and securing victory thanks to a break for 5-4 in the second followed by a quick service game which put him through in 66 minutes. So solid has the revitalised Roddick been all week that he has yet to face a break point in three matches. Isner, who lost early at the recent Montreal and Cincinnati Masters, continued to shore up his confidence with Monday's the start of the US Open fast approaching. The North Carolinian, who grew up just 50 kilometres away, fired a dozen aces and made a huge recovery after dropping the opening set in 22 minutes to Baghdatis, a former Australian Open finalist. Isner has taken his ace tally for the week to 39 and is pleased with how his big game is working. "I don't give guys a lot of rhythm, that's for sure," said Isner. "I play first-strike tennis and try to keep it on my terms. I want to keep the points short and mix things up a bit." Isner admitted he still has things to work on. "I didn't hit the slice so well today from either side, But this is the second time I've played him this summer and I've had good success," said the American, who beat Baghdatis in Montreal a fortnight ago. Isner trails Roddick 3-1 in their career series, with Roddick winning their last meeting in March in the third round at Indian Wells. Isner was blown away with two service breaks in the first set. But he dropped his serve just once more in the remainder of the contest, which ended in just under two hours as Isner converted his first match point. In the other two quarter-finals, third seed Alexandr Dolgopolov plays Dutch 10th seed Robin Haase and Sergiy Stakhovsky, who won the event last year when it was played in New Haven, takes on Frenchman Julien Benneteau.