NEW YORK, NY, USA - Two-time US Open runner-up Victoria Azarenka returned to the last eight in Flushing Meadows for the first time in five years, outlasting an in-form Karolina Muchova, 5-7, 6-1, 6-4.

"It was a crazy match," she said during her on-court interview. "She played unbelievably, getting to balls and bringing everything back. I would try coming to the net and bring passing shots where I couldn't do anything! It was such a great match and of such high quality. I really had to dig in and bring more aggression because she was really feeling the ball well.

"It was really tough, but also so much fun. I hope people had fun watching because I enjoyed playing it tonight."

Azarenka extended her winning streak to nine in a row after recovering from a set down to emerge victorious after two hours and 29 minutes on Louis Armstrong Stadium. 

Taking on the former World No.1 for the first time, Muchova, who reached her first Grand Slam quarterfinal last summer at Wimbledon and kicked off her US Open campaign with a win over two-time champion Venus Williams, broke serve to start the match and soon led by a double break at 4-1.

Azarenka has been in the midst of a career renaissance after capturing the Western & Southern Open - her first title since giving birth to son Leo in 2016 - and rolled into the second week of the US Open without dropping a set - avenging a 2019 loss to Aryna Sabalenka in the second round. Saving two set points, the Belarusian clawed back even at five games apiece, only for Muchova to break straight back and serve out the opening set.

"When you become a parent, you have a responsibility you didn't have before. You have to respond to that and learn about yourself. It's not just me teaching Leo; I feel he continues to teach me things about myself. Sometimes, I see some of his facial expressions and actions he makes, and it makes me think I should change my own so I don't see them from him. Children are like sponges; I'll say one word and he'll repeat it.

"That perspective translates to on-court. I want to do my best because my son is watching me now. He understands more, so I need to be a good example so he can grow up with good behavior and not breaking racquets. That might still happen, but we'll see!"

Under fire to start the second set, the two-time Australian Open champion saved a break point to hold on in the opening game, and began to take control, surging ahead to a 5-1 lead.

Serving to level the match, Azarenka got to set point when Muchova netted a forehand and forced a third set as the Czech youngster netted another.

The 24-year-old, who has been working with famed Czech coach David Kotyza, took a medical timeout ahead of the final set, and emerged with a heavy strapping on her left leg. 

A marathon third game saw Azarenka battled through five deuces to convert a third break point chance and move ahead by a break, only for Muchova to even the score with a smooth forehand up the line and moved ahead on serve at 3-2.

Azarenka responded with aplomb, managing a tight service game to amp up the aggression on return, striking a searing backhand to score three more break points, converting her second to move within two games of victory.

Muchova made a brave last stand, saving a match point as she served from the brink of defeat, but Azarenka was undaunted, earning three match points with an aggressive lob, and made it over the finish line with one last forehand winner.

"I know it's a difficult time for everybody in the world, and being able to have a Grand Slam tournament and do what I love to do, I'm just grateful for the opportunity to play. I don't take any day for granted and I want to enjoy all that comes my way."

In all, Azarenka played a cleaner match, striking 21 winners to 28 unforced errors; while Muchova made more winners, she also made more errors (32 to 45), and was broken six times as the Belarusian won nearly half the points played on the Czech star's return.

Standing between Azarenka and a first Grand Slam semifinal since the 2013 US Open is No.16 seed Elise Mertens, who stunned reigning Australian Open champion Sofia Kenin on Arthur Ashe Stadium.

"She's played great. She played very well at Cincinnati, so it's going to be fun. I've played her once or twice in doubles, so it'll be great. It's another amazing opportunity to be in the quarterfinals of a Grand Slam."

2020 US Open highlights: Azarenka overcomes Muchova