NEW YORK, NY, USA - No.13 seed Maria Sakkari rallied from the brink of defeat to shock two-time Western & Southern Open champion Serena Williams, 5-7, 7-6(5), 6-1 to roar into a second straight Cincy quarterfinal.

"I haven't realized it yet," Sakkari said after the match. "It feels pretty good, because she has been a role model for me growing up, and obviously what she has achieved is huge. So it feels very nice."

Sakkari, who started the week with a decisive victory over in-form American teenager Cori "Coco" Gauff, trailed by a set and a break in her first meeting with the 23-time Grand Slam champion only to roll through the final set after two hours and 17 minutes on Grandstand court.

"I was not feeling good. This first set and a half, I could not feel my shots. There were some points where I was playing good, but I knew it was going to be ugly.

"I'm kind of proud of myself that I came through that match just because of my mentality and my fighting spirit."

Williams, who was two points from defeat in her opening round against Arantxa Rus, arrived to court after a late-afternoon storm delayed action for 90 minutes, but enjoyed a seamless start - racing ahead 5-2 on the strength of an early break of serve.

Sakkari, who began 2020 with a first Grand Slam second week run at the Australian Open, soon settled and capitalized on some loose shots from the No.3 seed to level the set at five games apiece. Looking to avoid another tie-break, Williams turned the tables on the 25-year-old to sweep the final two games.

Shaking off the halted momentum, Sakkari began the second set with another break, moving ahead 3-1 before Williams regained her bearings, reeling off the next four games to find herself serving for the match.

Williams, who reached the last eight in her return to action at the Top Seed Open presented by Bluegrass Orthopaedics with a win over elder sister Venus, was two points from victory when Sakkari stepped in to earn a late break point and level the set once more.

As in the opening set, Serena responded with a solid service hold to put the pressure back on Sakkari, who forced a tie-break with a hard-fought hold of her own.

The ensuing Sudden Death saw Sakkari reverse a 4-1 deficit as Williams struck some tentative shots from the baseline, and the No.13 seed was first to set point with a big serve. With a deciding set in sight, Sakkari struck a booming forehand to level the match.

She maintained that aggressive form early in the final set, striking another impressive winner to engineer break points in Williams' first service game. What followed was a topsy-turvy series of seven deuces before Sakkari ultimately converted her eighth opportunity. 

"I think the key point was, of course, winning the second set, but then serving the way I did first game of the third set was just like a turning point for me, because it gave me a lot of confidence going into the third set."

Sakkari took total control from there, surging ahead 5-0 as frustration and physical struggles set in for the former World No.1.

"It was tough," Serena said after the match. "I literally should have won that match. There was no excuse. It was hard, but I had so many opportunities to win, and I have to figure that one out, like how to start winning those matches again. There is really no excuses, to be honest.

"I started cramping, but I shouldn't have been in that situation. I don't think that helps mentally when it's like, you know the match is over and you have won the match, and now your legs were already tired and now they are even more tired, and now it's even more tired.

"I literally put myself in this situation. You know, it's like dating a guy that you know sucks. That's literally what I keep doing out here. It's like I have got to get rid of this guy. It just makes no sense. It's frustrating."

She nonetheless saved seven match points as she served to stay in the match, battling bravely from the back of the court.

With the match on her racquet, Sakkari struck a searing forehand and at last made it over the line on her eighth match point.

In all, the No.13 seed made two more winners (27 to 25) and 15 fewer errors (43 to 58), converted five of 19 break point opportunities while maintaining a 59% first serve percentage, striking seven aces to Williams' nine.

Standing between Sakkari and a third Premier 5 semifinal is British No.1 Johanna Konta, who eased past former World No.2 Vera Zvonareva in straight sets earlier in the day.

"I haven't watched her playing this week, but I assume she's playing really good from her results," Sakkari said.

"It's going to be a tough match. Now I just cannot think of the way she plays. I don't remember. It's too early and too soon. I just need a good dinner, good night's sleep, and then figure out how to play her tomorrow after breakfast!"

2020 Cincinnati Highlights: Sakkari solves Serena