Serena Williams' smooth progress at the Amelia Island Championship in Amelia Island, Florida came to an abrupt end on Friday when she retired from her quarter-final against Italy's Silvia Farina Elia with a sprained ankle.
"I was running for a ball and totally twisted my ankle," Serena said after withdrawing from the event when her 12th seeded opponent squared their match at a set apiece.
"Things just spiralled downward from there. Of course I wanted to finish the match, but I obviously couldn't move very well and wasn't able to do it."
It proved to be a bad day for the Williams sisters as Venus faded in her quarter-final against world number one Lindsay Davenport, who took a step closer to a third title here with a gritty 1-6, 6-3, 6-4 victory.
Following Thursday's rain-affected programme, several players were required to play twice and Davenport showed her battling qualities as she recovered to beat her American compatriot.
However, most of the drama surrounded Serena.
With a television crew watching her every move for a reality show about the sisters, Serena outslugged France's Mary Pierce 7-6, 6-4 in a third-round encounter, rallying from 5-1 down to win the first-set tiebreaker before snatching the second thanks to a single break of serve.
Returning to action for their last four encounter in the night session, Farina Elia's variety and clever use of angles often had Serena screaming at the sky.
The Italian held two set points when serving at 5-4, but Serena fought back and broke twice to take the opener 7-5.
Farina Elia led 3-0 in the second but Serena rallied again to lead 4-3 and looked on course for victory, only to suffer a sprained left ankle chasing a ball when leading 5-4.
After treatment, Serena played on and even held three match points in the tiebreak but Farina Elia hit back to level and the American duly retired.
"I am very, very happy because it's the first time I beat Serena," she said.
"I was really scared when she fell because I thought it was really bad and that it was her knee. But that was also difficult for me because she came up with some good shots and I got really tight."
DAVENPORT RECOVERS
Earlier, Davenport had to dig deep to beat Venus, having been blown away in the first set.
"She definitely played well in the first set," Davenport said.
"I got a bit lucky in the second, I was down 15-40 a couple of times and managed to pull out two sets without really playing that well."
For 25 minutes it was vintage Venus, but as the match wore on so the mistakes increased, and Davenport took advantage to set up a clash with seventh seed Nadia Petrova of Russia, who beat 15th seed Shinobu Asagoe of Japan 6-0, 0-6, 6-2.
Asagoe had earlier caused the biggest upset of the event as she shocked third seed and French Open champion Anastasia Myskina of Russia 7-6, 7-6.
"I think I just made mistakes at the wrong time," Venus said.
"I feel like I played well, it was one of my best matches this year, everything's getting better."
Virginie Razzano of France continued her giant-killing run, following up her second-round win over fourth seed Alicia Molik with two more victories over seeded players.
The world number 54 ousted 13th seed Ai Sugiyama of Japan 6-4, 6-7, 7-5 and then stunned sixth seed Vera Zvonareva of Russia 6-4, 6-4 to set up a semi-final against Farina Elia.
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