The Serb third seed will face a Spanish clay craftsman in number two Tommy Robredo, who had his own troubles in overcoming Argentine Agustin Calleri 7-5, 6-7 (5/7), 6-3.

Richard Gasquet and Paul-Henri Mathieu set up a French showdown after both subdued stubborn opponents.

The young pair will meet for the second time this season following a January quarter-final in Sydney with the score standing at 2-0 in Gasquet's favour.

Gasquet overcame a slow start to advance past crafty American veteran Vince Spadea 6-3, 6-4.

Mathieu, ranked 42nd and winner of a title last week in Casablanca, had his own struggle before overcoming Argentine Juan Monaco 6-4, 4-6, 6-1.

But Mathieu admitted he's well worn down after stretching his current win streak to eight matches with his victory over Monaco.

"It won't be the best way to go into this match, especially against Richard," he said. I've played a lot of matches. I have to somehow be at 100 percent to try and beat him."

Djokovic needed five match points to finally stake his claim on the semi-fials in his Estoril appearance.

The youngster says he will need all of his energies to push for the final.

"It was good to win a tough one, but it's a minus for tomorrow," said the world number five. "I hope to recover as much as possible.

"There was a lot of tension in the match and my movement was not so good, it led to unforced errors. Conditions are tough here and I need all of my strength when I play Tommy,"

Robredo avenged a loss to Calleri from last week in Barcelona as he won his 19th match of the season.

Gasquet improved to 21-8 on the season after reaching a Monte Carlo quarterfinal in his first clay outing of the pre-Roland Garros campaign.

"I didn't know his game, so it was difficult for me at the start," said the winner.

"He was in the Top 20 a few years ago and is a dangerous player.

"I began badly and was lucky to win this match in straight sets. It will be tough to play a countryman in the semifinals.

"We are good friends and know each other's games well. It will be anyone's match."

Among the women the number three Lucie Safarova was the last seed standing in the semifinals.

Spain's Nuria Llagostera Vives reached the last four as French top seed Marion Bartoli was forced to retire with a strained abdominal muscle, losing 6-2, 3-1.

The winner will face German Greta Arn, who beat Sweden's Sofia Arvidsson 6-2, 6-2.

In the bottom half, Czech Safarova advanced at the expense of Spaniard Lourdes Dominguez Lino 7-5, 6-3 and will next play Viktoria Azarenka of Belarus, who beat last weekend's Budapest champion Gisela Dulko of Argentina 6-1, 6-2.

"It was a tough match for me, she's a good player," said Safarova, 30th in the world and winner in Estoril in 2005. "She played a huge topspin to my backhand that was hard to return.

"I had to wait for my chance to hit winners. I'm just happy to win and reach the semifinals."