WASHINGTON, DC, USA - France's Kristina Mladenovic will play in the quarterfinals at the Citi Open for the third time in her career following a 6-4, 4-6, 6-3 victory over teenage wildcard Hailey Baptiste in the second round on Wednesday night.

The former World No.9 was pushed all the way by the 17-year-old American, playing just her second-ever WTA main draw match after having upset No.2 seed and former US Open finalist Madison Keys in Tuesday's opening round.

Related: 'I knew every other person in the crowd': Hometown teen Baptiste advances at Citi Open

Despite 11 double faults, Mladenovic saved seven of the nine break points she faced over two hours and five minutes, and broke Baptiste's serve four times to advance to her fifth quarterfinal of the season.

"It was definitely not an easy match. I think she deserved her spot in the second round. I was not surprised that she had such an amazing win in the first round. I could see her potential and her qualities," Mladenovic said.

"It's never easy to face someone you've never actually saw, so it's tough to know what to expect, what are her best shots and patterns in the key moments, so it takes a little while.

"She competed very well. She has a big serve and very heavy spin. I think I didn't play my best, but there were a lot of things to work for and to stay composed.

"I'm just very glad I found the solution, stayed composed and showed my experience."

There was little to separate the two players in the first two sets, despite Baptiste sitting at World No.283 in the rankings - over 200 places below her French foe.

After dropping serve in the fifth game of the opener, Baptiste rallied to draw level at 4-4 before ultimately falling behind by a set, but finally delivered in the clutch in the late stages of the second set.

After missing out on her first six break point chances in the second set - three in the second game, one in the eighth and her first two set points - Baptiste finally converted her seventh overall opportunity in the set, and broke Mladenovic in the 10th game to extend the match.

Ultimately, though, the 26-year-old's experience saw her through to the last eight in the third set, as she lost just six points in four service games and never faced a break point.

The World No.49 scored the decisive break of the decider early on, as she broke the teenager from a 30-0 deficit in the third game, and was hardly challenged on serve from that point on. 

The Frenchwoman, who has not reached a semifinal in 2019, next faces Russian qualifier Anna Kalinskaya, who upset No.8 seed Monica Puig in over two-and-a-half hours earlier on Wednesday, 2-6, 7-6(5), 6-4.

With unseeded Americans Christina McHale and Jessica Pegula dueling in the other quarterfinal, an unseeded finalist is guaranteed out of the bottom half of the draw.

"She's also an upcoming player. She's quite young, but the difference compared to today is that we actually faced each other twice before, so it's not completely unknown territory," Mladenovic said.

"I will have my game plan ready. I'll rest, and have a good day of practice tomorrow. She fought her way through qualies and now she's in quarterfinals.

"Everybody who's still in the tournament is showing good form, so I'm looking forward to it."