WIMBLEDON, England — Five-time champion Roger Federer outclassed Mario Ancic — the last man to beat him at Wimbledon — in straight sets today to reach the semifinals and extend his grass-court winning streak to 64 matches on the first day of significant rain delays at the All England Club.

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Riding his dominant serve and punishing forehand, Mr. Federer put on a masterful performance to beat Mr. Ancic 6-1, 7-5, 6-4 and move another step closer to becoming the second man in history to win Wimbledon six years in a row.

Mr. Federer served 15 aces, and finished with three straight in the final game — including with a second serve on match point. He won 61 of 71 points on serve, including his last 16, for his 39th straight win at Wimbledon.

“I’m playing great, serving excellent,” said Mr. Federer, who hasn’t dropped a set all tournament. “Many aces is always helpful. Some rain delays broke my momentum a little bit. I got back into the match and played really well all the way through.”

Mr. Federer will next face Marat Safin, who served 18 aces and overcame Feliciano Lopez 3-6, 7-5, 7-6 (1), 6-3 to become the first Russian man to make the Wimbledon semifinals in the 40-year history of the Open era.

In the bottom half of the draw, No. 2 Rafael Nadal edged closer to a third consecutive Wimbledon final against Mr. Federer by blowing away Britain’s Andy Murray 6-3, 6-2, 6-4.

“I played probably my best match for sure here,” said the four-time French Open champion, who didn’t face a break point and, like Mr. Federer, hasn’t been broken in five matches.

Mr. Nadal, bidding to become the first man to win the French Open and Wimbledon in the same year since Bjorn Borg in 1980, will have to wait an extra day to find out who he’ll face in the semifinals.

The quarterfinal between 94th-ranked Rainer Schuettler and No. 145 Arnaud Clement was suspended at one set apiece because of fading light. Schuettler won the first 6-3 and Clement took the second 7-5.

Mr. Federer was at his vintage best, holding serve at ease and gliding across the court and ripping shots that flew past Mr. Ancic or forced him into errors. He has reached the semifinals for the 17th consecutive time at a Grand Slam event.

“I really feel like I’m playing as good as the last few years,” the 12-time Slam champion said. “I’m on such a great winning streak on grass. I feel so comfortable on Centre Court. My confidence level is really high.”

Mr. Safin, a former top-ranked player who won the 2000 U.S. Open and 2005 Australian Open, has slipped steadily in the rankings over the last three years and came into the tournament at No. 75.

The Russian got off to a rocky start against left-handed Mr. Lopez, and was down 5-2 in the first set when play was suspended by rain. Even though he ended up losing the set, Mr. Safin stepped up his game after the break and took command. Mr. Lopez double-faulted on set point in the third-set tiebreaker and served his sixth double-fault on match point.

“I was too nervous to play well in the beginning,” Mr. Safin said. “I got a service break and played better. I had to calm down. I was too nervous to make anything happen.”

After the start of play was held up by nearly an hour, Mr. Federer walked onto Centre Court in his custom-made cardigan just after 1:45 p.m. and glanced up at the threatening skies.

It looked like he wanted to get things over as quickly as possible against Mr. Ancic, who beat him in the first round of Wimbledon in 2002, a year before Mr. Federer began his run of five titles. That match was replayed on the BBC during today’s rain delays.

“I’ve played many matches since,” Mr. Federer said. “All I remember is the match point. It’s one of those things you just try to forget.

Mr. Federer charged through the first set in 20 minutes — winning 12 of the first 14 points, hitting six aces and winning 16 of his 17 service points. The two were 1-1 in the second set before the rain came again and the covers were rolled back onto Centre Court.

They resumed play 2 hours, 10 minutes later, and the two kept holding serve with ease and looked headed toward a tiebreaker until Ancic wobbled and Federer broke for a 6-5 lead. From 30-30, Mr. Ancic handed the game to Federer with three straight errors — two missed backhand volleys and a double fault on break point.

Mr. Federer promptly served out the set, closing with a 129 mph (208 kph) ace down the middle.

The first game of the third set was a 16-minute marathon — only four minutes shorter than the entire first set. The game went to deuce 10 times and Mr.Ancic saved four break points before finally converting on his seventh game point with a forehand volley winner, holding up a clenched left fist.

But it was only a matter of time for Mr. Federer to break again, and he did for 3-2 when Mr. Ancic sailed a forehand long. That was enough as Mr. Federer closed it out five games later.

In the seventh game of the set, Mr. Ancic ducked and dropped to his knees to get out of the way of a Mr. Federer forehand that whizzed past his head at the net. A smiling Mr. Federer walked around the net to say he was sorry, and Mr. Ancic playfully tossed a ball at him.

Other than a 1 hour, 41 minute rain delay at the start of play last Friday, Wimbledon had basked in remarkably good weather until now.

Venus and Serena Williams, who between them have won six of the last eight Wimbledon titles, are one round away from a third women’s title matchup and seventh Grand Slam championship showdown.

Next up for two-time champion Serena in tomorrow’s semifinals is Zheng Jie, who became the first Chinese player to reach the semifinals of a Grand Slam. Defending champion and four-time winner Venus will next face No. 5 Elena Dementieva.