(6) Belinda Bencic def. (Q) Eugenie Bouchard 6-7(7), 6-1, 6-4
By ranking alone, World No.14 against World No.506 would not ordinarily ring alarm bells. But in this instance, it was also a battle between two former Top 5 players, with reigning Olympic champion Bencic resuming a rivalry that dates back to juniors with former Wimbledon finalist Bouchard.
The match proved to be worthy of top billing as Bencic of Switzerland needed all of her skills to fend off Canada's Bouchard in 2 hours and 39 minutes.
Bouchard won their junior match at Roehampton in 2012, but Bencic is now 3-0 against Bouchard in the pros, with her two prior WTA wins both coming in 2015.
Bencic had her hands full from the start against Bouchard, who qualified for the main draw and is playing just her fifth event of the year as she returns from injury. Bencic saved three set points before holding her own set point at 7-6 in the first-set tiebreak.
However, Bouchard got to 7-7 with a backhand crosscourt winner and after a netted return by Bencic at 8-7, Bouchard was one set away from her first Top 20 win in over five years.
But Bencic showed off the form that brought her a gold medal last year in the second set, racing through it in half an hour. A break for 3-2 in the third set put Bencic further along the path to victory.
Bouchard, though, continued to match Bencic with sterling angled winners, and the Canadian held two break points at 5-4. Bencic swatted those away, and after a series of exceptional rallies in the final moments, Bencic converted her second match point as one final groundstroke found the baseline.
Bouchard finished the match with six aces to Bencic's two, but the Canadian was 1-for-4 on break points, while Bencic converted four of her 12 break points.
Aliaksandra Sasnovich def. (8) Jelena Ostapenko 6-2, 6-2
World No.31 Sasnovich notched her first win over former Roland Garros champion Ostapenko with a 1-hour and 13-minute upset.
Sasnovich had lost all four of her previous meetings against World No.16 Ostapenko, but she won 60 percent of points returning Ostapenko's first serve on her way to victory.
It marks Sasnovich's third Top 20 win of the season, with her previous two coming in back-to-back wins against Emma Raducanu and Angelique Kerber en route to the Round of 16 at Roland Garros.
Sasnovich will next meet another Grand Slam titlist, when she faces reigning Wimbledon champion Elena Rybakina in the Round of 16. Rybakina has won both of their previous meetings in straight sets.
(Q) Caty McNally def. (Q) Anna Blinkova 6-1, 6-2
McNally took 1 hour and 12 minutes to triumph in an all-qualifier showdown. The 20-year-old American won 80 percent of her first-service points and 75 percent of her second-service points, and was never broken in the match.
To earn a spot in her second WTA quarterfinal of the year, McNally will have to take down either No.7 seed Beatriz Haddad Maia or Czech hope Karolina Muchova, who will play their first-round match on Wednesday.