TORONTO, Canada - Czech qualifier Marie Bouzkova scored the biggest victory of her career to date in the second round of the Rogers Cup on Tuesday night with a 6-2, 7-5 upset of No.7 seed and 2018 finalist Sloane Stephens. 

The victory is far and away the World No.91's best win terms of ranking, as the 21-year-old had previously been 0-7 against Top 50 players in her young career so far.

"I honestly still can't believe it. Coming through the qualies, I got comfortable on the court," Bouzkova said on-court after the match.

"Today, I just tried to fight for every ball, and somehow, I got the win."

Playing just her second-ever match against a Top 10 player after losing to compatriot Karolina Pliskova at the Brisbane International to begin the season, Bouzkova broke Stephens' serve five times over the course of one hour and 41 minutes.

Though the 2017 US Open champion seemed to make a last stand as she broke Bouzkova when she first served for the match in the 10th game of the second set, the Czech would not be denied her fourth straight win of the week.

The former US Open champion could never find her feet against the Cezch's defenses in the match, as she racked up 48 unforced errors to just 29 winners, as Bouzkova totaled 10 winners to 14 unforced.

"I'm feeling great. I didn't expect this today. I just went out there, trying to enjoy and fight for every ball," Bouzkova said. 

"I played well. I felt comfortanle on the court and I'm happy to get the win. I think I was defending well today. Sloane is such an aggressive player.

"Even though she tried to take off her pace a little, I stayed there, and tried to play aggressive as well without making too many unforced errors and just going for it."

Up next, the Czech will face the winner of the match between Jelena Ostapenko and Anastasia Pavlyuchenkova, the latter of whom served an upset of her own on Tuesday with a three-set victory over No.9 seed Aryna Sabalenka, 3-6, 6-3, 7-5.

"I've played Ostapenko in juniors and I've never played Pavlyuchenkova, but I've obviously seen both of them on the TV a lot," added Bouzkova. "I guess I'll watch a little bit of their match tomorrow and get ready for Thursday."