Martina Hingis' long reign as world number one came to an end at the Porsche Grand Prix when an ankle injury forced the Swiss star to retire from her semi-final against Lindsay Davenport.
She needed to beat Davenport to stay ahead of Jennifer Capriati when the WTA releases the new rankings on Monday.
The Swiss star may need surgery on damaged ankle ligaments, ruling her out for six weeks.
That is effectively the remainder of the season and includes the year-ending WTA Championship in Munich.
Capriati was delighted to cap an amazingly successful season by reaching number one in the rankings.
"It's like a dream. I'm speechless," said the 25-year-old.
"When I retire, I will be able to say to myself that I was once the number one - even if it's just for one day, it's great."
The injury occurred in the third game when Hingis fell over after lunging for a shot on her backhand side.
Hingis went on to lose the game and called on the trainer to tape her ankle during the break.
Hingis attempted to carry on, but was forced to pull out after just two more points.
Lindsay Davenport admitted the injury looked painful.
"I talked to her after her ankle was taped and asked if she was sure she could play," Davenport said.
"She said she just wanted to try but that it really hurt."
Davenport now faces Belgium's Justine Henin in Sunday's final.
The sixth seed overcame the challenge of Jennifer Capriati's conqueror, Sandrine Testud, 6-3 7-6.
The only time Henin was in trouble was in the fourth game of the second set when she had to fight off two break points.
She maintained her composure to save both and hit an ace to hold serve.
Results from Saturday's Porsche Grand Prix action:
Lindsay Davenport (USA, 3) bt Martina Hingis (Swi, 1) 2-1ret
Justine Henin (Bel, 6) bt Sandrine Testud (Fra) 6-3 7-6 (7-3)
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