Fifth-seeded Elena Dementieva of Russia upset the injured Venus Williams 6-3, 5-7, 7-6 (3) Wednesday in the quarterfinals of the Nasdaq-100 Open.
Dementieva also struggled but overcame a match point to win the sloppy contest.
"It was a very difficult, long, but I think interesting match," Dementieva said.
In men's play, No. 3-seeded Guillermo Coria of Argentina and No. 21 Fernando Gonzalez of Chile advanced, and will play an all-South American semifinal Friday. Coria beat unseeded Nicolas Kiefer of Germany 6-3, 6-3, and Gonzalez rallied past unseeded Andrei Pavel of Romania 6-7 (5), 6-3, 6-4.
Williams took a nine-minute injury timeout when she rolled her right foot in the final game of the second set. She actually played better when the match resumed, winning 14 of 17 points to take a 3-0 lead in the last set.
Serving for the match at 5-3, Williams hit four double-faults, including three in a row to lose the game. She held a match point at 6-5 but sailed a forehand long, then committed five unforced errors in the tiebreaker.
"It was sunny and the wind kept blowing and my toss got crazy," she said. "That was not good."
The errant serves didn't surprise Dementieva.
"I just said to myself, `She's just like you, you know, she can be nervous,'" Dementieva said with a laugh.
The match was dramatic but unsightly. Each player double-faulted 11 times and lost serve six times. Williams committed 51 unforced errors, Dementieva 34.
Slowed by injuries since last summer, Williams has slipped to No. 17 in the rankings and has played only 10 matches in four events this year. never advancing beyond the quarterfinals. Seeded second at Key Biscayne, the three-time champion was unable to take advantage of a field missing the world's five highest-ranked players, including No. 1 Justine Henin-Hardenne of Belgium.
Williams' defeat spoiled a potential renewal of her sibling rivalry with younger sister Serena in the final Saturday. Instead, the No. 5-seeded Dementieva advanced to the semifinals Thursday, where she'll play No. 8 Nadia Petrova of Russia.
Petrova beat No. 21 Nathalie Dechy of France 6-2, 6-2.
Top-seeded Serena Williams will play No. 25 Eleni Daniilidou of Greece in the semifinals.
Venus led 6-5, 30-15 in the second set when she rolled her foot hitting a forehand, then bent over in pain as Dementieva smacked a winner. Williams limped to the corner, then back to her chair.
Williams later said she hurt her ankle, but the WTA Tour described the injury as a foot sprain. A trainer taped both the foot and ankle, and when play resumed, Williams won the next two points for the set.
She seemed bothered by the injury on only a few points the rest of the way.
"I was just thinking that she's a very good actress," Dementieva said. "She was moving much better after the break."
When told of Dementieva's comment, Williams responded: "Maybe I should talk to her. I clearly twisted my ankle and I had issues there. If that's the way she feels, that's fine. These days, in order to be a champ and to be a winner, you have to play under all circumstances, and I think that's what I did."
Dementieva held her own in rallies, but her serve -- long the weakest part of her game -- became progressively worse. Serving at 5-6 in the final set, she double-faulted twice and lobbed in several second serves at under 70mph, but still managed to hold.