Chennai: World No.4 and top seed Stan Wawrinka stayed on course to defend his singles title with a 6-2, 7-6(4) win over Gilles Muller and set up a semi-final clash with Belgian David Goffin in the ATP Aircel Chennai Open here Friday.
Fourth seeded Goffin, among the most improved players last season and ranked 22, eased his way past Austria's Andreas Haider-Maurer 7-5, 6-2.
Earlier, World No.15 Roberto Bautista Agut of Spain overcame sixth seeded Yen-Hsun Lu of Chinese Taipei who blew set points in the first, 7-6(7), 6-4, and will take on qualifier Aljaz Bedene of Slovakia whose dream run continued in the tournament.
Bedene, the 25-year-old ranked 156, who upset second seed Feliciano Lopez Thursday, knocked out another Spaniard Guillermo Garcia-Lopez, the fifth seed, 2-6, 6-3, 6-2, on the outside court.
Eight seeded Muller, the 31-year old southpaw who jumped from 368 to current 46 in rankings last year, started off badly, twice dropping his serve to lose the first set in quick time.
However, the match was quite close in the second set with Muller changing tactics by coming more to the net behind his serve and displaying more aggression. Muller broke Wawrinka in the sixth game, but the Swiss promptly neutralized with a break back in the seventh.
Although Muller served better than he did in the first set, a host of double-faults weighed him down, but with Wawrinka committing some uncharacteristic errors, especially on his otherwise strong backhand, the game went with serve leading to the tie-break.
Wawrinka, winner here last year and 2012, reserved his best for the last as he won the final three points with a ripping backhand crosscourt winner followed by two aces, the last a 213 kmph thunderbolt.
"The conditions were a bit tricky and windy. Muller has a big serve and being a lefty and all that. But I am happy the way I finished. I made some mistakes in the second set, but after breaking back, I played aggressively," said Wawrinka.
There was little to separate 26-year old Bautista Agut, the third seed, and Lu, popularly known as "Rendy" on the tour as both came up with some amazing shots from the backcourt, but the Frenchman's superior courtcraft settled the issue.
The 38th ranked Lu, playing some excellent tennis, broke Bautista Agut in the seventh game, but the Frenchman broke back in the 10th, saving a set point in the process to force the tie-break.
Lu, 31, the first and only player from his country to break into top 100, was ahead 2-0 in the shootout, but Bautista Agut hung in there and eventually won 8-7 for the first set with the Taipei player wasting a couple of set points.
An early break of serve put Bautista Agut ahead and the Frenchman, growing in confidence, pressed home the advantage to run out deserving winner.
"Straight sets yes, but we were on court for nearly two hours. Lu is a good player and he had his chances in the first set, but I stayed with him. It gave me a lot of confidence and an early break in the second set helped me win the match," said Bautista Agut.
Singles (quarter-finals): 1-Stan Wawrinka (SUI) bt Gilles Muller (LUX) 6-2, 7-6(4); 3-Roberto Bautista Agut (FRA) bt Yen-Hsun Lu (TPE) 7-6(7), 6-4; 4-David Goffin (BEL) bt Andreas Haider-Maurer (AUT) 7-5, 6-2; Q-Aljaz Bedene (SLO) bt 5-Guillermo Garcia-Lopez (ESP) 2-6, 6-3, 6-2.