Federer was severely tested by wildcard Gil

Roger Federer overcame the weather and Frederico Gil to book his place in the semi-finals of the Estoril Open.

The world number one had his serve broken in both sets by Portuguese wildcard Gil in a match that was twice interrupted by rain delays.

But he returned from the second rain delay to secure a hard-earned 6-4 6-1 win over the world number 146.

The top seed, seeking his first title of 2008, will play German Denis Gremelmayr in the semi-finals.

"Conditions were tough, you play in heavy conditions, the rain comes, you leave the court and come back and you change quite a bit," said the world number one.

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"There was a lot of wind as well. I didn't know my opponent at all, I'd never seen him play. That made it tricky.

"He played well for set and a half. Thank God I came back from the second rain delay and had the right game plan. I had to play a really good match today to win."

Federer is working with Spanish coach Jose Higueras in the build-up to the French Open.

The players were forced off for 35 minutes in the first set and when they came back, Federer broke to go 4-2 up.

Gil broke back only for the Swiss star to claim the set as skies began to darken.

Federer lost his rhythm and his serve to start the second set before breaking straight back to level at 1-1.

The players were forced off for another 25 minutes before returning and Federer twice broke as he closed out a difficult victory with his fifth ace.

Second seed Nikolay Davydenko took his winning streak to 10 matches with a 6-4 5-7 6-3 win over Frenchman Marc Gicquel.

Davydenko, who won the Miami Masters earlier this month, admitted he was so exhausted after losing the second set, he felt unable to continue.

"I just told myself that I should try and see if I could fight," said the world number four.

The Russian now faces another Frenchman Florent Serra, who crushed Italy's Flavio Cipolla 6-1 6-1.