Victoria Azarenka prevented the first over-30 women semi-final lineup in Grand Slam history, ripping Daniela Hantuchova 6-2, 6-3 on Wednesday to secure a US Open last-four match with Italy's Flavia Pennetta.
The 24-year-old second seed from Belarus took only 76 minutes to defeat the 48th-ranked Slovakian while 83rd-rated Pennetta reached her first Grand Slam last four by ousting 10th-seeded compatriot Roberta Vinci 6-4, 6-1.
World number one Serena Williams, seeking her 17th Grand Slam title and fifth US Open crown, will meet Chinese fifth seed Li Na, the 2011 French Open champion, in Friday's other semi-final at Arthur Ashe Stadium.
Williams, Li or Pennetta would become the oldest US Open women's champion by winning the title at age 31. Australian Margaret Court owns the mark, having been 55 days beyond her 31st birthday when she captured the 1973 crown.
"It's great to see such great players out there and have the chance to play against them," Azarenka said.
"It's amazing to see athletes playing so much longer so fans can enjoy them longer. People are really taking care of their bodies and it's really taking the sport to the next level."
Azarenka, who lost to Williams in last year's final, has won the past two Australian Open titles and beat Williams in the final of a tuneup event in Cincinnati, making her a big threat to dethrone her on the New York hardcourts.
Hantuchova would have made this the first women's Grand Slam final four in history with every participant over age 30 had she beaten Azarenka.
"I'm a baby. What can I say?" Azarenka said. "Since I came here as a junior I always play like a kid."
After an exchange of breaks to open, Azarenka broke on a forehand winner for a 2-1 lead and broke again in the seventh game for a 5-2 edge, then held with a forehand volley to claim the first set after 31 minutes.
Hantuchova broke Azarenka's first service game of the second set for a 2-0 lead but Azarenka won the next five games to seize command. She handed the Slovak a break on a double fault in the eighth game but broke back to win.
Hantuchova, in her first US Open quarter-final since 2002, reached her only Grand Slam semi-final at the 2008 Australian Open.
Pennetta is the fourth-worst-ranked US Open women's semi-finalist ever but has not lost a set and has dropped only 25 games in five matches. She has split two matches with Azarenka, winning their most recent meeting at Dubai in 2011.
Pennetta, who only avoided having to qualify for the US Open main draw after Kazakhstan's Yulia Putinseva withdrew with a back injury, made a breakthrough triumph one year after missing the event for right wrist surgery.
The injury is only now beginning to fade and allow Pennetta, who won only one hardcourt tuneup match, to recapture the form that saw her reach the US Open quarter-finals three times before.
"I feel really good," Pennetta said. "This is the first week where I feel better, feel like myself, maybe play better.
"I didn't play my best tennis the past six months. Everything is starting to feel more normal, the way it was before the injury."
The only lower-ranked women in a US Open last four were unranked 2009 winner Kim Clijsters, unranked 1979 semi-finalist Billie Jean King and 92nd-ranked German Angelique Kerber, a 2011 semi-finalist.
After an exchange of breaks in the first two games, Pennetta broke Vinci again in the fifth game of the first set but surrendered a break to equalize by netting a backhand in the eighth game.
"In the beginning we didn't play good tennis," Pennetta said. "I was tight. She was tight. The day was tough for both of us."
Pennetta won the next six games to seize command and ended matters on a forehand lob winner to advance after 65 minutes.
"After I won the first set I started to relax," Pennetta said. "I started to be more aggressive. My serve was working really good."
Vinci hit 14 winners but made twice as many unforced errors.
"It's tough to play against Roberta," Pennetta said. "I think she also feels the pressure. It's not easy to play one of your friends, but this is the tour."