WIMBLEDON, England — Novak Djokovic was upset in straight sets by Marat Safin in the second round at Wimbledon today, ending the Serb’s chances of testing his theory about Roger Federer’s vulnerability.

The 75th-ranked Safin won 6-4, 7-6 (3), 6-2 on Centre Court. It was a stunning loss for the third-ranked Djokovic, who came to the All England Club confident after beating top-ranked Federer in the semifinals at this year’s Australian Open en route to his first Grand Slam tournament title.

Top-ranked Ana Ivanovic, another Serb, also struggled, but won. The French Open champion saved two match points — including one that bounced off the net chord for a winner — in the second set before overcoming 29-year-old Frenchwoman Nathalie Dechy 6-7 (2), 7-6 (3), 10-8.

Also on the women’s side, two-time champion Serena Williams advanced with a 6-4, 6-4 win over Urszula Radwanska on Court 2, the so-called “graveyard of champions” for its history of upsets.

The 21-year-old Djokovic came up against one of the toughest second-round opponents he could have drawn.

Former No. 1 Safin has won two Grand Slam titles. One came when he upset Federer in an Australian Open semifinal en route to the 2005 title. Safin beat Djokovic in the first round of that tournament — their only previous meeting.

“It was certainly a very bad day for me,” Djokovic said. “I didn’t do anything that I was supposed to — he was very solid in all segments.”

Djokovic had said Federer, bidding for his sixth consecutive Wimbledon crown, was vulnerable after his recent lopsided French Open loss to No. 2-ranked Rafael Nadal.

The hype surrounding those comments set up an enticing semifinal here. Now, it will be Safin who tries to go down that path.

Safin said he came in under the radar, with Djokovic under all the pressure.

“He’s the one who has to win matches. For me, nobody expects anything,” said Safin, who admitted he had not dared look beyond the second round. “Now, I’ll have to check — the way I’m playing now, I could go far.”

Djokovic seemed to be vulnerable himself, playing on a surface he is not entirely comfortable on and struggling with his serve in a blustery breeze. After saving three match points, he served a double-fault to give his Russian opponent a fourth, then double-faulted again to concede.

“I was serving a lot of double-faults, which is unusual,” said Djokovic, who was broken twice in each of the first and third sets and only broke Safin’s serve once. “I was just not finding my momentum.”

Ivanovic was erratic against a resilient Dechy, who saved two match points on her own serve in the 12th game of the third set.

Ivanovic set up three more match points at 0-40 in the 18th game and, after Dechy saved one, the 20-year-old Serb squealed with delight and kissed the net after hitting a forehand winner to end it in 3 hours, 24 minutes.

“It was an amazing match,” Ivanovic said. “In the second set I saved some match points and from that point on I just thought it’s my second chance.”

She said her heart skipped a beat when she won match point.

“Once it went in I just couldn’t believe it,” she said. “I’m just so, so thrilled.”

Ivanovic next plays China’s Zheng Jie, a 6-2, 7-5 winner over Britain’s Elena Baltacha.

Lleyton Hewitt, another former champion, also survived Court 2.

The only other Wimbledon champion in the men’s draw, Hewitt advanced 7-6 (4), 6-0, 6-2 over Albert Montanes of Spain that was much quicker than his opening five-setter.

In other women’s matches, Marion Bartoli, last year’s losing finalist, beat Tatiana Perebiynis 6-2, 7-5, fourth-seeded Svetlana Kuznetsova ousted Ukraine’s Kateryna Bondarenko 6-2, 6-3 and 2007 quarterfinalist Nicole Vaidisova dropped nine straight games to fall behind a break in the third set before recovering to beat Samantha Stosur 6-2, 0-6, 6-4.

After losing, Djokovic shook his head as he walked forward, and hugged Safin across the net. Djokovic said he might have had too much respect for Safin’s obvious but often erratic talent.

“Safin is a player who is known as a big talent, but again, he makes a lot of unforced errors,” he said. “I had opportunities, but I just made some unforced errors, which were really uncharacteristic, without any sense.

“Safin still has his ups and downs, and is known for his mental instability in some ways, but he’s still a great player. He wants to step it up again. (Today) he was mentally there.”

Grass is not Safin’s favorite surface, either. Wimbledon is the only major where he has not advanced beyond the quarterfinals. But he is a dangerous opponent now.

Federer is most at home on grass — he is on a 60-match winning streak on the surface. He had a potentially tough second-round match later Wednesday on Centre Court against Sweden’s Robin Soderling.

Another former No. 1, Juan Carlos Ferrero, had to retire with a leg injury in the third set when he was behind 6-4, 6-4, 2-1 to 20-year-old Mischa Zverev. Ferrero reached the quarterfinals last year before losing to Federer.