Serena Williams from the USA reacts prior to her second-round match against Na Li from China at the Porsche Grand Prix tennis tournament in Stuttgart, Germany, yesterday. Williams was eliminated. - AP

STUTTGART, Germany (AP)

Serena Williams' game collapsed after she swept the first set yesterday, leaving her with a 0-6, 6-1, 6-4 loss to China's Li Na that will cost her the No 1 ranking.

By dropping the second-round match at the Porsche Grand Prix, Williams will be overtaken by Jelena Jankovic when the new rankings come out Monday, the WTA said. The American gained the top spot when she beat Jankovic in the final of the US Open three weeks ago for her ninth Grand Slam title.

Jankovic plays her first match in the tournament today against Alona Bondarenko of Ukraine in the second round.

"Obviously, I want to be number one but I am not focusing on that," Williams said. "I am focusing on winning titles and that goes hand in hand (with getting No. 1). I am not worried, it will come again if I win tournaments. I play to win titles and Grand Slams, although obviously the No. 1 is also on my mind."

Williams was playing her first match since the US Open after getting a first-round bye in Stuttgart.

Turnaround

She rolled through the first set and appeared to be heading for a resounding victory when things suddenly turned around.

"I started making a lot of errors and I just gave it to her - maybe I started doubting myself," Williams said.

Li said she was so nervous at the start of the match, "I had such cold hands."

"I didn't have a chance in the first set," Li said. "But I looked at the clock and I saw it was only 20 minutes (into the match) so I told myself I could be winning in an hour. I knew I just had to hang in there."

Defeated Venus

Li also beat the elder Williams sister, Venus, while reaching the semi-finals at the Beijing Olympics. Venus Williams, who is still in the Stuttgart tournament, watched Serena's defeat yesterday.

Ranked No 30 in the world, Li wasted three match points at 5-3, then fell behind 0-40 in her next service game after Williams had held for 5-4. She then put in a service winner and followed with an ace. After successfully challenging a call that her serve was out to get it to deuce, she clinched the match with her third ace of the game.

Li missed 11 months with a rib fracture last year and right-knee surgery in March.

"I believe I can go into the top 10 if I stay healthy," she said.

Fourth-seeded Elena Dementieva, the Olympic gold medalist, advanced to the third round by beating Sybille Bammer 6-1, 6-4.