Estoril:Roger Federer battled changing weather, which went from sun to rain and back, before beating Portugal's Frederico Gil 6-4, 6-1 to reach the Estoril Open semi-finals.
A quarter-final twice interrupted by the unpredictable conditions sent the players off court for 35 minutes in the first set and another 25 in the third game of the second.
Federer, working to lift his first title of the season as he begins the pre-French Open clay campaign working with Spanish coach Jose Higueras, was able to come out after the second interruption to finish the job.
"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, now 14-4 on the season.
"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."
The top seed will now face Germany's Denis Gremelmayr, who beat Czech Jiri Vanek 6-2, 3-6, 6-2, for a place in the final.
Nikolay Davydenko stretched his spring win streak to ten matches as he joined Federer in the last four.
The Russian second seed, who won the prestigious Miami Masters title this month, fought past Frenchman Marc Gicquel 6-4, 5-7, 6-3 on the heavy clay.
Davydenko, who confessed that his mental strength is draining away after his run of form, will face Florent Serra of France, who beat Italy's Flavio Cipolla 6-1, 6-1.
Davydenko said he was so exhausted after losing the second set that he almost did not want to go on.
"I just told myself that I should try and see if I could fight," said the world number four.
In the women's tournament, second-seeded Russian Maria Kirilenko moved into the semis with a convincing win over Italian Tathiana Garbin 6-0, 6-1 while Czech Iveta Benesova defeated French eighth seed Camille Pin 3-6, 6-2, 6-3.