NEW YORK -- Serena Williams battled back to defeat fellow mother Tsvetana Pironkova and reach the semi-finals of the US Open Wednesday, as Daniil Medvedev booked his place in the last four.
Williams, seeded third, came from a set down to overcome the unseeded Bulgarian and keep alive her bid for a 24th singles Grand Slam title at Flushing Meadows.
Her comeback included two astonishing shots with her left hand that contributed to winning points.
"At that point I was fighting so hard. I was just trying to do everything I can whether righty or lefty," she said.
A sluggish start saw the American lose the first 6-4, but she fought back to take the next two 6-3, 6-2, in 2hr 12min inside Arthur Ashe Stadium.
"I'm happy to be standing here talking to you because at one point I think I was pretty close to not being here," Williams told an on-court interviewer.
"I never give up and you know I just gotta keep going," she added.
Williams smashed 20 aces, the most she has had in eight years, taking her tally for the tournament to 64 so far.
The record for the most number of aces in a US Open in the women's singles is 70, set by Williams in 1999 when she won for the first time.
"Sometimes when I'm serving, I just tell myself, I don't care if my arm falls off, I'm going to keep serving," she said.
Williams is looking to match Margaret Court's record for the most number of singles Grand Slam wins.
It has been more than three years since she won her 23rd at the 2017 Australian Open -- when she was already pregnant with daughter Olympia.
Williams has come close since, reaching four major finals only to come away empty handed.
Pironkova, herself a mother, only returned to tennis this year following a three-year absence from the circuit.
- 'Incredible' -
Pironkova's last tournament appearance had been the 2017 Wimbledon championships when she exited in the second round.
She gave birth to her son during her break from tennis but elected to return in 2020, only to see her comeback plans disrupted by the coronavirus shutdown.
Williams said she was in awe of Pironkova's run to the last eight, which included high-profile scalps such as 10th seed Garbine Muguruza.
"I couldn't even do that. I could barely win a match when I came back so she's incredible," Williams said.
Williams will play either former world number one Victoria Azarenka or 16th seed Belgian Elise Mertens on Thursday for a place in Saturday's final.
In the men's draw, Russia's Medvedev downed compatriot and childhood friend Andrey Rublev 7-6 (8/6), 6-3, 7-6 (7/5).
Twenty-two-year-old Rublev raced to a 5-1 lead in the first-set tie-break before Medvedev, last year's US Open runner-up, hauled back to win it 8-6 with an ace.
Medvedev, 24, smashed 16 aces and won 89 percent of first-serve points. He made 75 percent of returns to Rublev's 54 percent.
"One point decided two sets so it was a really tough match and Andrey was playing unbelievable actually," Medvedev said.
Medvedev will play either second seed Dominic Thiem or Australia's Alex de Minaur, seeded 21st, in the last four on Friday.
Fifth seed Alexander Zverev of Germany faces Spain's 20th seed Pablo Carreno Busta in the competition's other semi-final.
The disqualification of Novak Djokovic for accidentally hitting a line official with a ball during the last 16 means the US Open will crown a first-time Grand Slam winner on Sunday.
© Agence France-Presse