Atlanta - Gilles Muller ended his six-year ATP semi-final drought on Friday with a straight-sets upset of second-seeded South African Kevin Anderson at the Atlanta Championships.
The 28-year-old Muller, who won his sixth career Challenger title last May on grass but has been beaten in the only two ATP-level finals he has played, fired 14 aces and mustered one break of serve en route to a 7-6 (7/3), 7-6 (7/3) victory over Anderson.
Muller next faces either third-seeded American John Isner or Taiwan's Lu Yen-Hsun.
Muller was pleased to make a breakthrough after more than two and a half years of toiling on the lower-level Challenger circuit as he tries to improve his 82nd ranking.
The European missed on three break points in a game against Anderson in the closely contested match, but raised his game in the tiebreakers.
Muller is competing in just his third ATP tournament of 2011 after coming back from a knee injury and falling from the Top 100 in recent seasons.
He was playing his first quarter-final since the 2008 US Open, where he got into the field as a qualifier and eventually lost to Roger Federer.
He last made an ATP semi-final at Los Angeles in 2005.
"This feels good after playing for so long at Challengers," said Muller, who twice saved double break points against his serve. "It was tough serving, with the sun in your face from one side of the court.
"I had to change my toss, but I got some aces on break points and that helped. This week is important for the confidence. When you save break points you know you can also win.
"I know I can beat a lot of top players when I play well. The problem has always been consistency. Now that I'm in the semis, I hope I can play even better."
In the day's other two quarter-finals, top seed and defending champion Mardy Fish was to take on Indian eighth seed Somdev Devvarman while American teenager Ryan Harrison plays Rajeev Ram, who beat Lleyton Hewitt in the second round.