Venus, the eighth seed, went down 7-6 (3), 6-4 to fourth-seeded Ana Ivanovic on Wednesday, a day after defending champion Serena lost to No. 3 Jelena Jankovic.
Ivanovic, who never had taken a set off Williams in four previous meetings, is into the semifinals for the third time at a Grand Slam and next will face first-timer Daniela Hantuchova, who beat Agnieszka Radwanska 6-2, 6-2 in a Wednesday quarterfinal.
Jankovic will meet No. 5 Maria Sharapova in Thursday’s semifinals. Sharapova ended top-ranked Justine Henin’s 32-match winning streak with a 6-4, 6-0 win Tuesday.
Hantuchova had not been to the second week of a Grand Slam since her quarterfinal exits at three consecutive majors, ending with a loss to Venus in the Australian Open in 2003.
“It feels great. I kept fighting for every point, even in matches I wasn’t playing very well,” she said. “I kept believing I could do it, and here I am.”
Venus was in the second week at Melbourne Park for the first time since 2003, when she lost to Serena in the final.
She squandered a service break in the second set and had double-break point in the last game before Ivanovic reeled off four straight points to advance.
Serena fell 6-3, 6-4 on Tuesday to Jankovic, who reached the Australian semis for the first time and only the third time in a major.
Serena was unseeded and ranked No. 81 when she made her stunning run to a third Australian and eighth Grand Slam title here a year ago, punctuating that with an emphatic 6-1, 6-2 win over Sharapova in one of the most lopsided Grand Slam finals.
That loss stung Sharapova, who wants to make amends.
“Even though I beat Justine, it’s definitely not over,” she said. “I still have a lot of business to take care of.”
Sharapova, who struggled with a shoulder problem for most of last year, started returning to her best at the WTA championships in November before losing in three sets to Henin in 3 hours, 24 minutes - among the dozen longest women’s matches in the Open era.
She turned the tables in only 1:38 on Tuesday, inflicting the first 6-0 set on Henin since 2002.
“I really felt like I was in a bubble,” No. 5 Sharapova said. “I think it was one of the most consistent matches where I did all the things I wanted to do, and I did them correctly from the beginning to the end . . . and just played the way I can play.”
Henin, who struggled with her serve and was broken five times by Sharapova, said she had a minor concern over a lingering knee injury but put the end of her winning streak down as an inevitability.
“It’s very hard to be at your best level all the time,” she said.
Sharapova will be looking back for lessons to take into the semis against Jankovic, her old tennis academy pal.
Another Serbian player has a chance of making the semis, with No. 3 Novak Djokovic playing David Ferrer of Spain in the men’s semifinals. Two-time defending champion Roger Federer went against No. 12 James Blake in the night match. Blake is 0-7 against Federer, who beat him in the 2006 U.S. Open quarters.
No. 2 Rafael Nadal, the only player to beat Federer at the last 10 Grand Slams, advanced to his first Australian Open semifinal with a 7-5, 6-3, 6-1 win over No. 24 Jarkko Nieminen.
Nadal will play Jo-Wilfried Tsonga, who beat No. 14 Mikhail Youzhny 7-5, 6-0, 7-6 (6) late Tuesday.
