Venus Williams failed to capitalize on a match point and lost her Acura Classic quarter-final to Anna Chakvetadze as the No. 3 seed earned a 6-7 (5), 7-6 (3), 6-2 victory on Friday.
Chakvetadze squandered the first set after leading 5-2. The Russian double-faulted eight times in the match, three times giving games to Williams in the set. Included in that span was a set point that No. 10 seed Williams saved before going on to win the set in a tiebreak.
Chakvetadze trailed 5-3 in the second set before bouncing back. Williams held a match point at 5-4 before Chakvetadze broke serve. Both players held serve to force the tiebreak, which was won by Chakvetadze as she took advantage of several errors by the US player.
The 20-year-old Russian handled Williams easily in the final set to beat the Wimbledon champion.
"It was the biggest win in my career, but I am already thinking about tomorrow," Chakvetadze said. "I was fighting until the end. I think that was why I won."
Chakvetadze will face No. 1 seed Maria Sharapova in the semi-finals after her compatriot defeated India's Sania Mirza 6-2, 6-1.
"I'd rather take these matches than be playing 7-6 in the third set out in the heat," Sharapova said.
"From the beginning of the match, I played my game," said the world No. 2. "I did a really good job of serving well and stepping it up when I had to."
Patty Schnyder of Switzerland claimed another upset with a 6-4, 6-4 victory over No. 4 seed Nadia Petrova to advance to the other semi-final.
"She's a dangerous opponent with her big serve and her powerful groundstroke," the 11th-seeded Schnyder said. "For me, it was still a great win. I never expected to win it that easily."
No. 9 seed Elena Dementieva defeated fellow Russian Maria Kirilenko 6-2, 6-4 for a semi-final berth against Schnyder. Dementieva, a two-time Grand Slam finalist, lost to Schnyder in straight sets here last year in the semi-finals.
"I've never played against Maria before so I got a little bit nervous in the beginning," Dementieva said. "It was a quite difficult match even though the score was easy."
Schnyder was confident of making her first appearance in a final in more than a year.
"I'm feeling great out on the court," she said. "The last three days I know where my shots are going. Everything seems to be working. I just want to keep it up for the weekend."
Andy Roddick didn't need much of a scouting report before winning his spot in the semi-finals of the Legg Mason Tennis Classic by beating Lee Hyung-taik.
It was the second straight week he has defeated the South Korean in a quarter-final and the 7-6 (6) 6-2 victory took his career record against Lee to 10-1.
"He gets into a groove and sometimes you kind of just have to stay the course, wait for your opportunities," Roddick said. "I felt like I did a good job of that."
Roddick, who won here in 2001 and 2005, broke Lee twice in the second set after nearly losing the first.
In the tiebreaker, Roddick fell behind 5-4 but some unforced errors by Lee gave the opening set to the US player.
Roddick's semi-final opponent will be No. 7 Ivo Karlovic, who had 29 aces in a 4-6, 6-3, 7-6 (5) win over Paul Capdeville.
It's a match Roddick said could take a while.
"It's not going to be a lot of rallies. It's probably going to come down to a tiebreaker or two, a couple of points here and there," Roddick said. "With him it's difficult, sometimes you can play well and lose and sometimes you can play badly and win."