Italian compatriots, best friends and doubles partners Sara Errani and Roberta Vinci will battle for a semi-final spot after causing a couple of upsets in the women's draw.
Errani, the 10th seed, defeated last year's semifinalist and German sixth seed Angelique Kerber 7-6 (5), 6-3, while Vinci saw off Polish second seed Agnieszka Radwanska 6-1, 6-4.
It will be the first time two Italian women have made the last eight at the same Slam.
It also means that for the first time since 1930 an Italian woman will feature in the semifinal of the US Open. Baroness Maude Giacomo Levi was the last Italian in the final four of the tournament 82 years ago.
"I'm happy to play against her, for sure an Italian goes to the semifinal," Vinci said in a news conference. "She's my best friend, so I'm very happy to play against her."
Errani, 25, the French Open runner-up, made her first US Open quarterfinal in what has become her best year, which has brought her four singles titles and seven doubles trophies.
Vinci had lost all four previous meetings with Wimbledon finalist Radwanska.
The 29-year-old will be playing in a Grand Slam quarter-final for the first time.
"I just closed my eyes and played. The ball was big enough," she said.