NEW YORK, NY, USA -- Six-time champion Serena Williams of the United States staged a stellar comeback in her US Open quarterfinal match on Wednesday afternoon in Arthur Ashe Stadium, as she charged back from a set and a break down to end the magical run of unranked Tsvetana Pironkova of Bulgaria, 4-6, 6-3, 6-2.

No.3 seed Williams had to fight her hardest to pick up her Open Era-leading 106th match-win at her home Grand Slam event, eventually quelling the challenge of fellow mother Pironkova after two hours and 11 minutes of play and advancing to the US Open semifinals for the 14th time in her legendary career.

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"A match like today, I just feel like [Pironkova] was serving well, she was hitting winners everywhere," Williams said in her post-match press conference. "Maybe I wasn't being aggressive enough. So I think it's more or less me adjusting my game in the second set and coming back and just trying to do better."

In her 20th appearance at the US Open, Williams struck back from the loss of the first set to reach the semifinals for the 11th straight time in which she has contested the event. The 23-time Grand Slam champion fired a commanding total of 20 aces in the match, nearly half of her 44 winners. Williams also kept her unforced error total low, with 24, and just four of those came in the final set.

"It's not how you start; it's how you finish, right?" said former World No.1 Williams. "I just feel like, I'm okay. I'm ready to play three sets every match if I have to. It doesn't matter. A win is a win."

Pironkova had been the surprise package of the event, as she played her first tournament of any type since 2017 Wimbledon -- an absence of over three years after maternity leave, having given birth to son Alexander in early 2018. The Bulgarian racked up stirring wins in the early rounds as she romped to her fourth Grand Slam quarterfinal, but was unable to quell the Williams fightback in the last eight.

Williams will now face either Victoria Azarenka of Belarus or No.16 seed Elise Mertens of Belgium in the final four, as those two will battle for the last remaining semifinal spot on Wednesday night in Arthur Ashe Stadium. A meeting with fellow former World No.1 and resurgent mother Azarenka would be a rematch of the 2012 and 2013 US Open finals, both won by Williams.

However, Azarenka still has to get by Mertens to set up that encounter. The Belgian leads the WTA in match-wins this season, with 23 to her credit, including runs to the Prague final and the Western & Southern Open semifinals since the tour’s resumption of play.

"I just gotta be a little bit better, really, and just expect people to go lights out and just be ready for lights out," said Williams, looking forward to the semifinal showdown.

As the match kicked off, Williams slammed three aces in the opening game, but Pironkova replied in turn, starting with an ace of her own before holding for 1-1 with a forehand passing winner. More aces from Williams led to a hold for 2-1, but the Bulgarian remained unfazed as she held for 2-2 at love.

In the next game, the opening frame started to swing in Pironkova’s favor, where a double fault by Williiams gave Pironkova the first break point of the match. A well-struck ace by Williams erased that chance, but Pironkova gained another when the American shot a backhand miscue long. Pironkova took that second opportunity, converting for the break with a backhand winner.

Suddenly, the unranked Bulgarian began to ease through the set, claiming her service games with minimal fuss, including a hold for 5-3 with an ace. In the following game, Pironkova used two more superb backhands, one down the line and one lob, to garner two break points which doubled as set points, but Williams bravely powered those chances away to hold for 5-4 and extend the set.

But Pironkova did not flinch at the chance to serve out the set, cracking two strong serves in a row to grab two more set points. The surging unseeded player at last converted her third set point, grabbing the one-set lead with a winning crosscourt backhand.

Pironkova kept blasting brilliant backhands at perfect times at the start of the second set, as she forced an error off of that wing to break Williams in the opening game and earn a quick lead. However, the American was immediately able to at last get her footing in a Pironkova service game, as a rally on break point ended with a netted forehand by the Bulgarian to level the set at 1-1.

Williams then gritted her way through a tough, three-deuce service game to hold for 2-1, but Pironkova used her gutsy play as well to withstand a break point and hold serve in the next game. Williams, though, was serving her way through the second frame with relative ease, as she moved to a 4-3 lead without facing a break point since the first game of the set.

In the next game, Williams, bolstered by a brilliant left-handed return to force an error at 0-15, saw her best chance to take a commanding lead by zipping to triple break point. On her second opportunity of that trio, a lung-busting rally was ended with a netted forehand by Pironkova, sending both players into visibly emotional reactions as Williams took the crucial 5-3 lead.

Williams said the lefty return "was intense. At that point I was fighting so hard, I don't know. Actually been hitting a little lefty in my practice, but not on purpose."

"I noticed the other day, I hit a lefty shot and I was just in practice being super intense, and I guess it came through in the match," Williams smiled. "When you're in a position like that, and I was just trying to stay, this is the quarterfinals of a Grand Slam, and I was just trying to do everything I can whether righty or lefty."

Serving for the set, Williams slid behind 15-30, but the American extricated herself from that situation with three thunderous aces in a row to close out the game and level the match at one set apiece.

The third set started with a protracted game, as both players fought to start the decider with the momentum. After staving off two break points, Pironkova misfired on a backhand on the fifth deuce of the lengthy tussle, giving Williams her third chance to break. The American grabbed that opportunity with gusto, firing a forehand winner to close out the game and start the set with a bang.

"I think that was definitely a really important game, because I was able to break her," said Williams. "Although I was still holding serve, it would have been a different match serving at 5-4 as opposed to serving at 5-2."

Williams had to power through a close service game of her own to consolidate for 2-0, but after that, it was smooth sailing on serve for the American for the rest of the day, only dropping two further points on her delivery.

Pironkova kept herself only one break back through 4-2, but the Bulgarian missed a game point before falling further behind to Williams, after the American shot a backhand crosscourt winner to break for 5-2. Now firmly in control, a love hold sealed victory for the American, and Williams had locked up another classic comeback win on home soil.

2020 US Open highlights: Serena surges past Pironkova into semifinals