ESTORIL, Portugal (AFP) - 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 on Friday.
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 provisional 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 hope conditions hold while outsiders Jiri Vanek of the Czech Republic and German Denis Gremelmayr fight for the right to face the 12-time Grand Slam winner on Saturday at the Estadio Nacional.
Weather is not expected to change markedly for the rest of the weekend, turning the first week on European clay into a test of nerve and patience as well as becoming a pointer to the unfolding pre-Roland Garros run-up.
Federer went up a 4-2 break in the opening set against the 146-ranked Gil, a wild card entry with two wins this season at the ATP level.
But the underdog recovered before Federer claimed the set with another break as the skies began to darken again.
The Swiss lost his rhythm, losing serve to start the second set before getting it straight back at 1-1.
As another shower arrived, the pair left the court, coming back in sunlight just under half an hour later to complete the match.
Federer left little to chance, with two more breaks as he closed out the difficult victory with his fifth ace.
"I don't expect to win 6-0, 60-0, he's in the quarters and had to beat some players," said the world number one. "He's playing on home soil also, that makes it more difficult ever for me.
"You expect a player ranked where he is to maybe give you some mistakes and be a bit nervous. But it was only after second rain delay that I felt I had the edge."
Second seed Nikolay Davydenko was aiming to join Federer in the last four as he faced French seventh seed Marc Gicquel.
Davydenko, the recent Miami Masters champion, has won his last nine matches and holds a 2-0 margin over Gicquel.
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.
