Rotterdam - Top seed Roger Federer reached the Rotterdam Open semi-finals on Friday with a 7-5, 7-6 (7/2) win over Jarkko Nieminen, his 13th win in 13 matches against the Finn.

The Swiss star will next face unseeded Russian Nikolay Davydenko, who shocked fifth seed Richard Gasquet of France 7-5, 6-3, for a place in his first final of the season.

Gasquet had his chances through a 5-2 lead in the second set but double-faulted to 5-all allowing Davydenko win through in 97 minutes with five breaks of serve.

Nieminen, who won the Sydney title in January but was hampered at the Australian Open by an abdominal muscle injury, pushed 16-time Grand Slam winner Federer hard.

"It was a relief to come through. I played well on my serve but Jarkko made me work," said Federer after reaching his fourth Rotterdam semi-final.

"Jarkko did his job well, he's a good friend of mine and a good guy, always very fair. I've got a good record against him but every time he makes you work.

"I'm one more match into the tournament and I'm playing better as time goes by."

In Friday's other quarter-finals, Tomas Berdych, the Czech second seed, beat Andreas Seppi of Italy 6-3, 6-4 and next meets Argentine third seed Juan Martin Del Potro, who eased past Viktor Troicki of Serbia 6-0, 6-1.

Berdych completed his 67-minute victory over the 45th-ranked Seppi on a fifth ace of the afternoon at the Ahoy stadium, after breaking the Italian three times to take his indoor record to an unblemished 8-0 this season.

But the second-seeded perfectionist was slightly annoyed after losing serve for the only time in the match in the second set, a mistake which he quickly rectified to get the contest back on level-pegging.

"I played a good match but I'm not happy with that error," said the world number seven, who was unable to play his Rotterdam quarter-final a year ago after coming down with a fever.

"I was trying to keep my level high and I did it to save that one game. But I still managed to win in two sets, so it's all okay at the end.

"Of course, I have hopes of winning the tournament but it is one match at a time for me," added the winner of the Montpellier title earlier this month.

Berdych next meets Del Potro who has won his last two meetings with the Czech, both played in 2009.

"Berdych has been playing well for the last two years, according to the ranking, he would be the favourite in our match," said Del Potro, ranked tenth to his opponent's seventh.

"He has confidence and is a danger on this surface, I'll just concentrate on my game."