PARIS - Serena Williams is usually the one who saves match points, not wastes them.

Who seizes control of an exchange, not cedes it.

Who turns up her game at Grand Slam time.

Except at the French Open, the lone major tournament she's won only once and where she's now gone seven years without even reaching the semifinals.

The No. 1-ranked Williams dropped 17 consecutive points during one stretch, climbed all the way back to within a point of victory, then faded late and lost to No. 7 Samantha Stosur of Australia, 6-2, 6-7 (2), 8-6, on Wednesday in the Roland Garros quarterfinals.

"Had I played better for two minutes, maybe the result could have been different. But it didn't work out," said Williams, who missed a forehand by an inch or so when she held a match point at 5-4 in the final set. "Just wasn't playing well today. Last year, I choked. I guess it's a redundant story with me."

The upset was Stosur's second in a row - she eliminated four-time champion Justine Henin in the fourth round - and came a day after men's No. 1 and defending champion Roger Federer was stunned by Robin Soderling.

"It's not over yet," said Stosur, a tour-best 19-2 on clay this season. "I want to definitely try and keep going."

In keeping with the run of surprises at this French Open, No. 22 Jurgen Melzer of Austria came back to beat No. 3 Novak Djokovic, 3-6, 2-6, 6-2, 7-6 (3), 6-4, in the last men's quarterfinal.

Melzer, at 29 the oldest man left, never before won a match after losing the first two sets - and never made it beyond the third round at any Grand Slam tournament in 31 previous tries.

His reward? A semifinal Friday against four-time champion Rafael Nadal, who eliminated No. 19 Nicolas Almagro, 7-6 (2), 7-6 (3), 6-4.

Nadal, who lost to Soderling in last year's fourth round, extended his winning streak on clay to 20 matches.

In one women's semifinal Thursday, Stosur will play No. 4 Jelena Jankovic, who got past unseeded Yaroslava Shvedova of Kazakhstan, 7-5, 6-4. No. 5 Elena Dementieva will face No. 17 Francesca Schiavone in the other.

Williams never hid her frustrations against Stosur, who wore her usual white baseball cap and red-rimmed wraparound shades as the sun returned after several days of clouds and rain. Williams admonished herself aloud, sometimes muttering, sometimes screaming.

"I definitely was nowhere near my best today," Williams said, then added: "But she played really well."

About an hour after that loss, Williams went back on court to team with her older sister Venus and reach the women's doubles final by beating Liezel Huber and Anabel Medina Garrigues, 2-6, 6-2, 6-4. That victory means Serena Williams will top the WTA rankings in singles and doubles as of next week.