Italian veteran Flavia Pennetta reached the US Open semi-finals for the second time in three year, outsmarting fifth seed Petra Kvitova 4-6 6-4 6-2 to add to the Czech's Flushing Meadows frustration.
The Italian flag will feature prominently in the semi-finals with the 33-year-old Pennetta joined in the last four by 32-year-old compatriot Roberta Vinci, who booked her spot with a victory over Frenchwoman Kristina Mladenovic.
"I was just trying to fight every ball, running and trying to push the most I can," the Italian said. "The second set I was really in trouble, but I was just keep going, playing and playing. It's unbelievable."
Pennetta has always been at home on the New York hardcourts having now advanced to quarter-finals or beyond in six of her last seven visits to the National Tennis Center.
The same courts, however, have not been kind to Kvitova, the two-time Wimbledon champion, who never ventured past the fourth round until this year.
Kvitova, one of only two players to beat Serena Williams this season, had reached the quarter-finals without dropping a set.
The Czech had looked well on her way to a first semi-final appearance when she easily took the opening but the veteran Pennetta kept her cool on a sizzling day in New York.
Serving at 5-4 in the second Pennetta wobbled, missing an easy winner to hand Kvitova a break chance but the Italian didn't buckle and hung on to level the match and then dominated the third set as Kvitova wilted in the heat.
Meanwhile, Serena Williams kept her bid for a calendar-year grand slam on track, powering past big sister Venus 6-2 1-6 6-3.
Serena moved into the semi-final, just two wins from history, in what proved her toughest test so far.
The Williams sisters had met 26 times before but never with so much riding on the result.
A win by Venus would move her a step closer to a first grand slam since 2008 Wimbledon but would scuttle Serena's chances of joining their sport's most exclusive club of calendar-year grand slam winners which comprises just three members, Maureen Connolly, Margaret Court and Steffi Graf.
The buzz around Arthur Ashe Stadium was like that of heavyweight title fight and the action on the court was much the same as Serena and Venus put family ties aside and slugged it out like sworn enemies.
"She's the toughest player I ever played in my life and the best person I know," said Serena. "So it's going against your best friend and at the same time going against the greatest competitor for me in women's tennis, so it was really difficult."
Serena seized control early in the third and rode the momentum to the finish and a final four meeting with unseeded Italian Vinci who dug deep to beat Mladenovic 6-3 5-7 6-4.