NEW YORK -- American wild card Alison Riske forced a third set against Daniela Hantuchova, but the veteran pulled away for a 6-3, 5-7, 6-2 victory.
Hantuchova rocketed 15 aces (to two for Riske) and had 46 winners (to only 17 for Riske).
Roberta Vinci will face a fellow Italian in quarterfinals for the second straight year.
In a testament to the depth among Italy's women's tennis players, the 10th-seeded Vinci will also be taking on a countrywoman for the third straight round at this year's tournament. She and Flavia Pennetta both won Monday to set up a matchup of 30-somethings who have known each other since they were 8.
Vinci beat Camila Giorgi 6-4, 6-2 in 67 minutes. Moments later, rain started pouring down, stopping all matches at Flushing Meadows for 4 1/2 hours.
The delay couldn't have come at a better time for Pennetta, who came back to the court to seize momentum and clinch a 6-2, 7-6 (3) victory over 21st-seeded Simona Halep.
Halep had set point on her serve, trying to send the match to the third, when the skies opened up. Once they resumed, the 83rd-ranked Pennetta won three straight points to even the second set at 5-5.
Halep promptly broke again, but she couldn't serve out the set this time, either. Then the 31-year-old Pennetta dominated the tiebreaker for her first Grand Slam quarterfinal since 2011.
Vinci had never made a Grand Slam quarterfinal before this tournament a year ago, when she was 29. Now Vinci has done it in consecutive U.S. Open trips. She lost to another countrywoman, doubles partner Sara Errani, in the quarters in 2012.
"It's obvious that I'm not young. I'm 30. But it can be a strength, because I have a lot of experience," Vinci said. "Against a player like Camila, who is very young, it can be an advantage for me -- and I think it was on the court today."
Errani, the top-ranked Italian woman, was upset by Pennetta in the second round this year while seeded fourth. No matter, the country will still have a representative in the women's semifinals for the second straight time.
Before last year, that hadn't happened once in the Open era, which began in 1968.
Giorgi, a 136th-ranked qualifier, was trying to reach her first major quarterfinal at age 21. In her third-round upset of sixth-seeded Caroline Wozniacki, she crushed the ball on point after point, with 46 winners and 45 unforced errors.
She jumped to a 4-1 lead in the first set Monday, but Vinci stayed poised and patient. Vinci, who had never faced the younger Italian before, started attacking her forehand, and Giorgi's mistakes mounted. She finished with 35 unforced errors to 20 winners.
"The problem wasn't the opponent," Giorgi said. "The problem is that I wasn't myself on court today."
Vinci is one of only two players seeded in the top 10 left in her half of the draw, along with No. 2 Victoria Azarenka.
Azarenka's meeting with 13th-seeded Ana Ivanovic was postponed Monday because of the rain. So was the Williams sisters' doubles match.