New York - Italy's 83rd-ranked Flavia Pennetta has advanced to the final four at a Grand Slam for the first time by beating 10th-seeded compatriot Roberta Vinci 6-4, 6-1 in a US Open quarter-final on Wednesday.
Pennetta, the fourth-worst ranked of any US Open women's semi-finalist ever, will next face the winner of a later match between Belarus second seed Victoria Azarenka and Slovakia's 48th-ranked Daniela Hantuchova.
Pennetta, who has not lost a set in the tournament and has dropped only 25 games in five matches, owns a 3-2 career edge against Hantuchova and has split two matches with two-time reigning Australian Open champion Azarenka.
Top-ranked defending champion Serena Williams and Chinese fifth seed Li Na will meet in Friday's other semi-final at Arthur Ashe Stadium.
Williams, Li or Pennetta -- all 31 -- would become the oldest US Open women's champion by winning Sunday's final.
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.
"It's amazing," Pennetta said.
"I'm really happy. I can't believe it."
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."
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.
Pennetta won the next six games to seize command, breaking back to lead 5-4 when Vinci sent a forehand beyond the baseline and holding to capture the first set when Vinci netted a backhand volley.
Pennetta raced to a 4-0 lead and broke again in the final game on a forehand lob winner to advance after 65 minutes.
"I started to be more aggressive," Pennetta said.
"My serve was working really good."
Vinci, whose only prior Slam quarter-final was last year when she was ousted by conmpatriot Sara Errani, 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."
Azarenka, who lost to Williams in last year's US Open final, defeated the American in the final of a tuneup event in Cincinnati and is seen as the top threat to end the world number one's US Open reign.
Hantuchova, whose only Grand Slam semi-final was at the 2008 Australian Open, would make this the first women's Grand Slam final four in history with every participant over age 30 if she upsets Azarenka.
US Open results on Wednesday (x denotes seeded player):
Flavia Pennetta (ITA) bt Roberta Vinci (ITA x10) 6-4, 6-1
Ivan Dodig/Marcelo Melo (CRO/BRA x10) bt Treat Huey/Dominic Inglot (PHI/GBR x16) 7-5, 6-3