Last year's runner-up Victoria Azarenka was a hard-fought fourth-round winner, while Chinese star Li Na secured a berth in her first-ever U.S. Open semifinal on Tuesday.
The second-seeded Belarusian stalwart Azarenka overcame 13th-seeded fellow former world No. 1 Ana Ivanovic 4-6, 6-3, 6-4 in just over two hours at Ashe Stadium in a match that was postponed because of rain on Monday at the USTA Billie Jean King National Tennis Center.
Ivanovic staved off two match points and broke Azarenka to pull within 4-5 in the final set.
In the next game, Azarenka broke right back after blowing a third match point before converting on a fourth when her Serbian counterpart netted one final two-handed backhand.
"I was, like, sleeping," Azarenka said. "I really had to wake up in the second set and try to fight for points.
"The match points were pretty bad. I really didn't go for my shots. I kept waiting for a mistake, and obviously it didn't happen."
Azarenka is now 5-2 lifetime against the 25-year-old 2008 French Open champion Ivanovic, including a victory in California last month.
The 24-year-old Azarenka will meet 30-year-old former top-10 star Daniela Hantuchova in a quarterfinal on Wednesday. The Slovakian Hantuchova edged out American fellow non-seed Alison Riske in three sets on Monday.
Azarenka and Hantuchova have split four career meetings, but the Belarusian has won the last two, including a win at Indian Wells earlier this season.
Azarenka is the two-time reigning Australian Open champion and lost to Serena Williams in last year's U.S. Open finale.
Meanwhile, a fifth-seeded Li fought off 24th-seeded Russian Ekaterina Makarova 6-4, 6-7 (5-7), 6-2 in 2 hours, 20 minutes. The Chinese slugger recorded two of her seven service breaks in the third set, while Makarova failed to break Li in the deciding stanza of their quarterfinal.
The 31-year-old Li was this year's Aussie Open runner-up to Azarenka and captured the French Open and was an Aussie Open runner-up in 2011. She'll now appear in her fifth career Grand Slam semifinal (3-1).
Li will meet the Williams-Carla Suarez Navarro winner on Thursday.
The 2013 U.S. Open champ will earn $2.6 million. The current world No. 1 Williams would claim an additional $1 million as a result of capturing the U.S. Open Series.