WIMBLEDON, England — When 17-year-old American Melanie Oudin concluded the biggest match of her life Saturday at Wimbledon, she had to ask where to find the exit from the court.

Still finding her way around the All England Club, Oudin has made her way into the fourth round. The qualifier from Marietta, Ga., pulled the biggest upset of the first week today by beating former No. 1 Jelena Jankovic, 6-7 (8), 7-5, 6-2.

The No. 6-seeded Jankovic struggled with the heat on a sunny, 82-degree afternoon, and took a 12-minute break after the first set. The 2008 U.S. Open runner-up also needed treatment for her left foot later, and was plagued by erratic groundstrokes while Oudin played with poise down the stretch and swept the final three games.

Five-time champion Venus Williams joined Oudin in the round of 16 by beating Carla Suarez Navarro 6-0, 6-4.

Oudin (pronounced Oo-dan') arrived in London with an 0-2 record in Grand Slam matches, and she had to win three qualifying matches to make Wimbledon's main draw for the first time. She's ranked 124th and will crack the top 100 for the first time after the tournament.

Playing on cozy Court 3, she wore down Jankovic in an arduous first set. Oudin failed to convert four set points, committing an unforced error each time. But when the 66-minute set ended, it was Jankovic who appeared on the ropes.

A trainer and doctor came on court to check Jankovic's pulse and blood pressure. She rested on a towel while being treated, and after several minutes sat up while ice was applied to her neck and midsection.

Jankovic played on, but the match turned when Oudin overcame a 5-4 deficit in the second set. She repeatedly won points with drop shots, punctuating winners with shouts of "Come on!" The teenager smacked a forehand winner on the final point, then raised her arms with glee.

Williams took charge early against the 34th-ranked Suarez Navarro, winning the first eight games. Bidding for her third consecutive Wimbledon title, the No. 3-seeded Williams will next play 2008 French Open champion Ana Ivanovic, who beat 2009 Roland Garros semifinalist Samantha Stosur 7-5, 6-2.

No. 9-seeded Caroline Wozniacki reached the fourth round for the first time by beating No. 20 Anabel Medina Garrigues 6-2, 6-2.

In men's play, No. 29 Igor Andreev and Tommy Haas won matches suspended overnight because of darkness. Andreev beat Andreas Seppi 6-1, 7-6 (5), 4-6, 7-6 (5). Haas defeated Marin Cilic 7-5, 7-5, 1-6, 6-7 (3), 10-8.

No. 20 Tomas Berdych eliminated No. 12 Nikolay Davydenko 6-2, 6-3, 6-2.

No. 4-seeded Novak Djokovic has advanced to the tournament's second week without fanfare. He doesn't mind one bit.

"I realize the situation that I am in right now," Djokovic said. "Andy Murray and Roger Federer are in the spotlight, and obviously they deserve to be in that situation, because they have been playing great tennis the last six, seven months.

"But you have to look from the brighter side. I think it's good. It kind of releases the pressure for me."

Djokovic said he played his best match of the week Friday, when he beat American Mardy Fish 6-4, 6-4, 6-4. In the round of 16 Monday, Djokovic will face unseeded Dudi Sela, the first Israeli man in 20 years to reach Wimbledon's fourth round.

Sela beat No. 15 Tommy Robredo 7-6 (8), 7-5, 2-6, 7-5.

As the first half of the fortnight winds down, most of the attention remains on Murray, seeking to become the first British man to win Wimbledon since 1936, and five-time champion Federer. They're on course to meet in the final, with big-serving American Andy Roddick considered the next-strongest title contender.

Federer advanced by beating Philipp Kohlschreiber 6-3, 6-2, 6-7 (5), 6-1. Murray and Roddick had third-round matches scheduled for Saturday.

As for Djokovic: Fish said the Serb is capable of a run at the championship.

"He seems to be kind of going along quietly," Fish said. "He's not making too much noise out there — kind of letting everyone talk about Roger and Andy, and the other Andy, kind of going about his business."

Djokovic was a Wimbledon semifinalist at age 20 in 2007, then won the Australian Open the following year. He has 13 career titles, two this year, and while he has never won a grass-court tournament, he was the runner-up at a Wimbledon warmup tournament in Germany two weeks ago.

He was in fine form against Fish, constantly pressuring with his return while facing only one break point.

"If I play like today, I think I have a good chance to get far in the second week," Djokovic said. "If I perform like that, there is no reason to underestimate me."