Top-seeded Juan Martin del Potro and Janko Tipsarevic won in straight sets on Friday to reach the semifinals of the Erste Bank Open.

Del Potro defeated Marinko Matosevic of Australia 6-2, 6-2 to line up a match against Gilles Muller of Luxembourg, while second-seeded Tipsarevic was leading 6-2, 4-2 when Aljaz Bedene of Slovenia retired with a left thigh injury.

It was Del Potro's second match since returning from a right wrist injury that sidelined him for over a month.

"I feel confident with my shots but I need to improve a little bit," the eighth-ranked Argentine said. "I would love to be in the final, but I need to serve well and find a way to break [Muller's] serve."

Del Potro saved a break point in his opening service game against Matosevic and two more while serving for victory, but was in control throughout the match.

Earlier Friday, Muller advanced after defeating Paolo Lorenzi of Italy 6-3, 6-4. Muller had 10 aces and used one break in each set to reach his second semifinal of the year.

Tipsarevic's match took just over an hour. Bedene, playing in his first career quarterfinal, won the first nine points on his serve in the opening set but lost the next four as he was broken at 2-2. Tipsarevic dominated from then on as Bedene became hampered by the injury and struggled to move.

"I would rather win in a normal way but it's good for me this time," the ninth-ranked Serb said. "I had a doubles match late last night and didn't get to bed until half past one."

Tipsarevic's chances of qualifying for next month's season-ending ATP World Tour Finals in London would be boosted by a good result in Vienna.

"I am ready, I am mentally fresh, I am hungry," Tipsarevic said. "I still feel there is room for improvement in my tennis. There are small things that you can add to your arsenal of weapons."

Tipsarevic will play either third-seeded Tommy Haas or Grega Zemlja of Slovenia for a place in Sunday's final.