MELBOURNE, Australia — Defending champion Roger Federer advanced to the quarterfinals of the Australian Open, extending his winning streak to 25 matches with a 6-2, 6-2, 7-6 (4) defeat of Marcos Baghdatis on Sunday.

Federer has won 48 out of his last 50 matches, and hasn’t lost since the second round at the Athens Olympics last August. He next faces four-time winner eighth-seeded Andre Agassi, who defeated No. 11 Joachim Johansson 6-7, 7-6, 7-6, 6-5.

Federer was broken in the fourth game but didn’t face another break point.

Baghdatis stunned Federer with some whipping crosscourt forehands and had support from a small but vocal group of Greeks and Cypriots who’d let off flares after his third-round win.

Top-ranked Federer beat Baghdatis at the last U.S. Open, the 19-year-old Cypriot’s only other appearance at a major.

After falling behind 3-0 in the tiebreaker, Federer reeled off five straight points and then clinched it on two forehand errors from the 2003 Australian Open boys champion.

“I enjoyed the battle for sure,” said Federer. “After I’ve won, it’s always good to battle it out and win it.”

Federer said he’d seen Baghdatis’ forehand at the U.S. Open, and knew he’d be scrambling.

U.S. Open women’s champion Svetlana Kuznetsova advanced, not surprisingly, by beating another Russian. Kuznetsova pounded 29 winners in a 6-4, 6-2 win over Vera Douchevina, who only had five.

Seven Russian women made the fourth round, including three Grand Slam winners.

Two are already out.

Second-ranked Amelie Mauresmo of France had a 6-2, 6-4 win over Evgenia Linetskaya in a mistake-prone match with 11 service breaks. Linetskaya held serve once in the match.

Mauresmo raced to a 4-0 lead. After Linetskaya broke her to make it 4-1, Mauresmo took a medical timeout, left the court and came back with her left thigh wrapped.

She had trouble on serve after that, dropping it once again in the first set and twice in the second, but held on to close with an overhead winner.

Kuznetsova was dragged into the headlines earlier in the week when a Belgian regional sports minister said the 19-year-old Russian star had tested positive for ephedrine, a stimulant commonly used in cold medicines, at a charity match last month.

The matter blew over when it was revealed ephedrine isn’t on the list of banned substances for tennis players in the offseason.

Fifth-ranked Kuznetsova could meet fourth-ranked compatriot Maria Sharapova, the Wimbledon winner, in the next round. Sharapova faced Italy’s Silvia Farina Elia. In other fourth-round women’s matches, seventh-seeded Serena Williams played No. 11 Nadia Petrova.

In men’s matches, No. 4 Marat Safin – a two-time runner-up in Melbourne – faced Olivier Rochus.

American doubles combination Bob and Mike Bryan nearly lost their third-round doubles match to 13th-seeded Israeli pair of Jonathan Erlich and Andy Ram. The Israelis led the third-set tiebreak 5-1 before the third-seeded Bryans rallied to 5-5, then later saved two match points to win 10-8 in the tiebreaker.

Third-round men’s action Saturday was highlighted by Lleyton Hewitt’s 6-2, 4-6, 6-1, 6-4 win over Juan Ignacio Chela in a match full of spit and venom.

Chela became angry when he thought Hewitt’s loud cry of “Come on!” was a bit too much celebration for an unforced error that resulted in triple break point in the fifth game of the fourth set.

He drove his next serve at Hewitt, even though this was a critical part of the match. Hewitt converted the break and Chela spat toward Hewitt when the players were switching sides.