Collins, Jabeur, Rybakina earn quarterfinal berths in Chicago

Eight is great for Danielle Collins: the American booked a spot in her eighth quarterfinal of the season with a 6-2, 6-4 win over Elise Mertens on Thursday at the Chicago Fall Tennis Classic. 

Seeded No. 10, Collins won seven straight games from 2-1 down in the first set en route to beating Mertens, seeded No. 7, for the first time in their careers, having first met at Wimbledon three years ago.

Despite being the first player to lose serve in the third game of the match, Collins ultimately broke Mertens seven times in victory: the Belgian struggled on serve overall, particularly in the opener. She racked up seven of her 10 double faults in the first set, where she landed just 45% of her first serves, but battled admirably in the second set after receiving a medical timeout early on.

"It's been tough conditions with the wind. I'm just trying to do my best," Collins said on-court after the match. "I think both of our serves weren't at our best, but she was still hitting it pretty big. I had a bit of pressure there, but luckily, I was able to pull through."

Later, she added: "I think I had good energy from the very beginning. I executed my game plan really well and was moving well. I think I've made some good adjustments the past couple of days with the conditions here. There's a lot going on around the courts, and the wind, the weather changing here and there, you have to make technical adjustments. You have to be flexible to be able to make those changes."

Stats of the match: An even 15 winners to 15 unforced errors helped Collins earn victory, as did a plethora of break point opportunities. She converted 7 of 13 chances she created in the match, while Mertens was 4-for-8.

Up next, Collins takes on Marketa Vondrousova for a spot in her fifth semifinal of the season. The Czech advanced by beating No. 16 seed Jil Teichmann, 6-4, 6-3, in a match between the two left-handers remaining in the draw.

"I think one of the biggest things I struggled with last year was being able to make deep runs with the physical challenges I was experiencing. Now, after having the surgery, it's just enabled me to play consistently, day after day, and have the confidence I can do it," Collins said.

"I think it's going to be a tough match... I'm just going to have to put up a good fight."

Jabeur rallies for revenge against Pegula, Rybakina edges Kudermetova

Also through to the last eight early on Thursday were No.5 seed Elena Rybakina and No.6 seed Ons Jabeur, who ousted Veronika Kudermetova and Jessica Pegula, respectively. 

For Jabeur, a 1-6, 6-2, 6-3 victory against Pegula was a role reversal of their quarterfinal match in Montreal earlier this year. In that match, Jabeur won the first set, 6-1, before losing 1-6, 7-6(4), 6-0.

From 40-0 up in the match's last game, Jabeur was nearly broken - she needed to save two break points - before sealing the 1 hour, 34-minute victory. 

"I'm very happy. It was kind of the same scenario of what happened in Montreal. I had three match points, but I know Jess plays really good and you have to earn every game, every point with her, and I'm glad I got this win this time," Jabeur said. 

"I started really slow. Starting the match, I think I was a little bit sleepy. I started to move my legs better, I started to put more balls in. After, it was really tight between us."

The Tunisian advances to her sixth quarterfinal of the season where she'll face top seed Elina Svitolina. The Ukrainian won her seventh straight match in Chicago with a straight-sets victory over Romanian Elena-Gabriela Ruse.

Read more: Svitolina sweeps into Chicago QF; Muguruza advances as Azarenka withdraws

In exactly 2 hours, Rybakina picked up a third career win against Kudermetova and second in the span of two weeks, 7-6(4), 7-5.

A 6-1, 6-3 victor against the Russian in the first round last week in Ostrava, Rybakina didn't have it all her own way in the rematch as she was broken in the first game of the opening set. 

The pair twice traded breaks in the first set, and Kudermetova later saved a set point en route to leveling at 5-5. However, Rybakina sprinted to a 5-1 lead in the tiebreak, and though Kudermetova nearly leveled by winning the next three points after the changeover, the No. 5 seed pocketed a one-set lead by winning both of the Russian's final service points.