Top seed Elise Mertens and No.8 seed Yulia Putintseva set up a quarterfinal clash at the Mubadala Silicon Valley Classic thanks to a pair of epic second-round victories on Thursday on the campus of San Jose State University. 

Mertens punched her ticket to the last eight of a tournament for the fifth time this year - and first since the Mutua Madrid Open in May - with a 6-2, 4-6, 6-4 win over Kristina Mladenovic, leveling her all-time head-to-head against the Frenchwoman to 3-3. 

Behind 38 winners and six breaks of serve, Mertens battled through her opening match at the tournament in 2 hours and 40 minutes, taken the distance after flirting with a straight-sets victory.  

"I'm very, very, very thrilled. I think I can still improve... but at the end, I just wanted to win so badly. Mentally, I was prepared for a battle, and I got the hours in today," Mertens said on-court after the match. 

Later to reporters, she added: "It was a very physical match. I didn't really find my rhythm well today... sometimes it doesn't come easy. I think in the second set, she started to feel the ball a little bit better with less mistakes.

"It's just important to win the last ball and to keep fighting as I did today. I'm just pleased that I got through this one."

Mertens previously reached the semifinals in San Jose back in 2018, where she lost to eventual champion Mihaela Buzarnescu. She and Putintseva will play for a third time - they've split two career meetings on hardcourts - as the Kazakh rallied from a set down to defeat Aussie Ajla Tomljanovic, 3-6, 7-5, 6-3. 

"She a very good defender. She has some good hands too, with a lot of a drop shots," Mertens assessed. "It will be a difficult task to get through her, but that's the way I have to play, to attack a little bit more than today."

Down a set and staring down a 0-40 deficit at 4-4 in the second, Putintseva found her patented fight to keep her tournament debut going: saving 10 of the 11 break points she faced from then on, the Budapest champion booked a spot in her first hardcourt quarterfinal since last summer's US Open.

In all, Putintseva saved 15 of the 17 break points she faced in the match, and totaled 33 winners to Tomljanovic's 20. 

"I just was keeping in mind that I had to stay there, be there every point. In the first set, I didn't start so well and felt like my ball was flying a little bit," Putintseva said after the match. 

"I managed to stay lower to the ground and just be a little bit more patient, use a little bit more angles, and I think it worked well. In the third set, I was feeling great and was able to bring my level a little bit higher and that's what gave me the lead. 

"But Ajla was playing really good, very solid tennis. I think it was a really great match today."

Mertens posts gritty win over Mladenovic to book QF spot: San Jose Highlights

Also through to the last eight by the close of the day session was No.2 seed Elena Rybakina, who rallied from a set down to beat American wild card Claire Liu, 2-6, 6-0, 6-2.

The World No.20, fresh off a fourth-place finish at the Tokyo Olympics games just five days ago, was slow to start in her tournament debut and lost serve twice in the first set.

"It was not an easy match. I knew that it wasn't going to be easy," Rybakina said in her on-court interview. "Claire played well and I needed more time to feel the ball, to adjust to all the conditions. It took me the first set, but then I started to serve better and played overall better. I'm just happy with my win today."

However, she broke Liu five times in the second and third sets to defeat the American for the second time in the span of just over a month and advance to her fifth quarterfinal of the season.

By the end of 95 minutes, Rybakina tallied 28 winners to 20 unforced errors, and never lost serve herself in the two sets she won.

"The serve was much better in the second and third sets. I actually felt that in the first set that I was doing the correct things and that it was just a few mistakes. It turned around completely," Rybakina sad later in her post-match press conference.

"In the second set, I focused a bit more on my serve and I hit a few good returns. After this, I felt like she dropped a little bit of her level on the first serve, so it was easier for me because she was serving more second serves. In the third, it's difficult to maintain the level, because I played a little bit risky in the second set, but I found my way and it was good."

Under the lights, No.7 seed Danielle Collins continued the day's theme of thrilling three-setters: in her first career match against former US Open champion Sloane Stephens, Collins rallied from a set down, and a break down early in the third, to advance 3-6, 6-4, 6-3 and face Rybakina.

Landing just 41 percent of her first serves in the opener, Collins was broken three times and lost the last four games to fall a set behind.

However, an early break of the Stephens serve at 1-1 in the second set helped propel her forward into a decider, where she rallied from 2-0 down and cap a 2 hour, 10-minute victory.

"I got off to not a bad start and then there were some bumps along the way. Playing against Sloane, and being the consistent player that she is, it required a lot more concentration on my part today than other matches that I played recently," Collins said in her on-court interview.

"It required hitting a lot more balls and more patience to win some of those tough points. When you're not playing at your ideal self, I think you have to walk yourself through step through step, and I just tried to make little improvements along the way, especially with the serving. I tried to get my first-serve percentage up. I saw the numbers in the first set and I wasn't happy about that.

"I'm a bit of a perfectionist so I get really locked in to what I'm doing, but luckily, piece by piece, I got myself into a better situation and made better decisions when it really meant something."