The match proved to be Tuesday's highlight in Beijing as the much-anticipated tie between Coco Gauff and Naomi Osaka ended in anti-climax when the latter was forced to quit at one-set all with a back injury.
From 3-1 down in the opening set, former No.2-ranked Badosa dominated in her first win over third-ranked Pegula.
"She's one the of the players I never want to face - she's very solid, hits very flat, changes very well direction," said Spaniard Badosa, who was 0-3 previously against the American.
"I prepared myself for a battle, but I think today everything worked pretty well.
"Every point was very important for me, especially against Jessica, because she can come back at any moment."
We'd say — wta (@WTA) @paulabadosa didn't come to play, but she clearly did 😤#ChinaOpen pic.twitter.com/Yvh1KU4BK6October 1, 2024
Badosa next faces 35-year-old Chinese Zhang Shuai, who continued her resurgence with a 6-4 6-2 win over Magdalena Frech of Poland.
Zhang entered the event on a 24-match losing streak and ranked No.595, but she's yet to drop a set in four matches this week. That includes eliminating US Open semi-finalist Emma Navarro in straight sets for her first win over a Top 10 player in two years.
Yuliia Starodubtseva of Ukraine also caused an upset, beating No.14-ranked Anna Kalinskaya 7-5 6-0.
The No.115-ranked Starodubtseva will play Gauff in the quarter-finals following Osaka's withdrawal.
The first meeting between the two grand slam champions in more than two years was finely poised when Osaka, who received medical treatment early in the contest, shook hands.
Gauff helped carry Osaka's bags off the court and then said: "It was a good match up until this point. I wish Naomi a speedy recovery. No one wants to win a match like this, especially one-set all.
"Overall I tried my best. It wasn't my best tennis."
It had been an encouraging week for Osaka, who was playing her first tournament under new coach Patrick Mouratoglou, and she was the better player for most of the two sets.
The Japanese star was within sight of victory when she broke the Gauff serve to lead 6-3 4-3 but she lost the next three games before calling it a day.
