Tipsarevic, Del Potro advance

Vienna - 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. He will now play Grega Zemlja of Slovenia, who scored 14 straight points to close out a 6-4, 4-6, 6-2 win over Tommy Haas.

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.

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."

Later Friday, the 70th-ranked Zemlja broke Haas' serve at 2-2 in the deciding set and did not drop a point afterward to reach his first career semifinal.

"This is a huge surprise, I didn't even expect to win my first round here," said Zemlja, who had to qualify for the main draw and who was 0-5 against top-20 players. "I played well. Now I have the confidence that I can beat the top players."

Zemlja had two breaks to win the opening set and rallied from 4-0 down in the second to level at 4-4 before Haas won it.

"He's a great player, I've watched him many times on TV," Zemlja said. "From 2-2 in the decider, his forehand became a little bit shaky."

Haas, who landed his 500th career win on the ATP Tour on Thursday, made 34 errors from the baseline.

"It was not easy playing someone you hardly know," the 20th-ranked German said. "Sometimes I didn't move enough so I wasn't positioned well to hit the ball. He had good returns so I hardly got any free points on my serve."