Top seed Juan Martin del Potro will face qualifier Grega Zemlja for the Austrian Open ATP title on Sunday after the Slovenian world number 70 stunned Serb second seed Janko Tipsarevic in Saturday’s semi-finals.

Argentina’s del Potro reached his second consecutive final in the Austrian capital as he defeated Luxembourg’s Gilles Muller 7-6 (7-4) 7-6 (7-5) in a duel which featured 33 aces.

Zemlja, meanwhile, pounced on an injured Tipsarevic to win 3-6 7-6 (7-5) 6-2 in just over two and a half hours in his first career semi-final.

Tipsarevic began feeling an old injury in his right shoulder in the second set as Zemlja climbed back into the contest.

The Serb was unable to stop his inspired opponent’s momentum as Zemlja won the second set after Tipsarevic gifted a double-fault for two set points.

In the third, Zemlja went up two breaks and earned the biggest win of his career on a second match point as a Tipsarevic forehand clipped the top of the net.

“I played a great match, it was really difficult in front of such a big stadium filled with people,” said the winner. “It was very emotional for me, it felt super.

“It was a tough match against a top player like Janko and it came down to the last point.”

Tipsarevic, who is chasing a place in the season-ending World Tour Finals in London next month, was disappointed with his performance.

“I was too passive, waiting for him to make mistakes,” said the second seed, “I haven’t felt my shoulder problem for the past 18 months but it suddenly started bothering me.

“In the second set I was struggling on serve, I didn’t have the freedom to toss, I was just throwing it up where it did not hurt. My disappointment is huge. I’ll go to Valencia (his next event) and see how the shoulder feels.”

Zemlja had knocked out Tommy Haas in the quarter-finals for his first top 20 win and will now play his first final after winning his debut ATP semi-final.

Sunday’s final will be the second consecutive year that the 2009 US Open champion gets a chance to lift the Vienna title having gone down in the 2011 final to Jo-Wilfried Tsonga.

“I’m showing a good level, but I still need to improve. I’m playing well, but you can always play better,” said del Potro, the holder of 11 ATP titles, the last of which came on clay at Estoril in May.

Del Potro is provisional seventh in the race for the eight-man London field while Tipsarevic is ninth with two weeks of the regular season remaining.

AF