ROTTERDAM, Netherlands – Second seed Juan Martin del Potro cruised into the semi-finals of the Rotterdam World Tennis tournament on Friday with a victory in straight sets against Finland's Jarkko Nieminen.

The Argentine won 6-3, 6-4, and will now face unseeded Bulgarian Grigor Dimitrov in the last four, after he came from a set down to beat Marcos Baghdatis earlier in the day.

Del Potro took just under 90 minutes to go through, racking up 10 aces along the way before sealing victory on his second match point as the Finn returned long.

“It was a difficult win, he's a lefty and hit his shots differently,” said the 2009 US Open champion, who is currently ranked seventh in the world, of his opponent.

“He was fighting all the time and I had to play my best game to go through.”

Dimitrov beat Baghdatis 6-7 (4/7), 7-6 (7/0), 6-3 in a performance that showed he is returning to the kind of form he produced at the start of the year, when he reached the final in Brisbane before losing to Andy Murray.

The Bulgarian had also beaten Baghdatis in three sets in that tournament, and he repeated the feat here.

He lost the opening set 7-6, but levelled the match by winning the second 7-0 in another tiebreak.

In the decider, Baghdatis fought to recover from 4-2 down and saved a match point in the eighth game to hold serve.

But the 41st-ranked Dimitrov clinched victory a game later on his second opportunity, as his opponent's return sailed long to end a contest that stretched over two and a half hours.

He advanced despite converting just two of 13 break-point chances over the course of the match.

Top seed Roger Federer, who is bidding to win the Rotterdam title for the third time, was due to play his quarter-final against Frenchman Julien Benneteau later.

The winner of that match will face either Martin Klizan of Slovakia or French fifth seed Gilles Simon in the last four. – Sapa-AFP