Winners of 14 Grand Slam doubles titles, including two US Opens, the Williams sisters were playing together for the first time in more than four years, the occasion attracting a capacity crowd to watch one of tennis's most successful partnerships take perhaps a final bow.

If it was indeed the last time the Williams sisters would stand shoulder-to-shoulder on court, the end came with little sentiment or emotion. The two greats embraced briefly at the net then stoically packed their bags, exited to a standing ovation and offered only a gentle wave to the cheering crowd.

Serena signalled her intention to retire in a Vogue article in early August, saying she was "evolving away from tennis" but never confirming the US Open as her final event.

But Flushing Meadows has not seen the last of Serena just yet, with the the 40-year-old back in action on Arthur Ashe on Friday for an eagerly anticipated third round singles clash with Australia's Ajla Tomljanovic.

Serena and her 42-year-old sister went down fighting, clawing back from 1-4 down in the second set before the Czech pair steadied the ship.

"Im still in shock that we won because this is the first time we played together," said Hradecka, quoted by AFP.

"I'm so sorry for you that we beat them but we are so happy that we did it."

Meanwhile, Azarenka triumphed against Marta Kostyuk 6-2, 6-3 in a match dominated by bitter exchanges over the conflict in Ukraine.

Last week, Belarusian star Azarenka was axed from an exhibition event aimed at raising money for the war-ravaged country.

Ukraine's Kostyuk had refused to take part in protest at the presence of Azarenka who she has criticised for a perceived failure to condemn the invasion of her home country.

Belarus is a close ally of Russia and has allowed Moscow to use its territory to launch attacks into Ukraine.

The tension between the two was evident at the end of their tie on Court 17 with Kostyuk offering just a touch of racquets instead of the customary post-match handshake.

"How did it make me feel? It's not the most important thing in the world right now," said Azarenka.

No handshake

Kostyuk, the 20-year-old world number 65, said a handshake would not have been appropriate.

"I genuinely wanted to warn her that I'm not going to shake her hand," she said.

"She never came up to me personally to tell me her opinion, what she thinks (about the war)."

Away from the controversy, world number one and French Open champion Iga Swiatek cruised into the third round with a 6-3, 6-2 win over 2017 champion Sloane Stephens.

Paula Badosa, the fourth seed and potential semi-final opponent of Swiatek, suffered another miserable return to the city of her birth.

The Spaniard's failure to get beyond the second round will stretch for another year after losing 6-7 (5/7), 6-1, 6-2 to Petra Martic of Croatia.

Sixth seed Aryna Sabalenka, a semi-finalist in 2021, came back from 1-5 down in the second set and saved two match points to defeat Kaia Kanepi, 2-6, 7-6 (10/8), 6-4.

China will have four women in the last 32 for the first time at a Slam after Zheng Qinwen defeated Anastasia Potapova and Yuan Yue got the better of Irina-Camelia Begu.

Zhang Shuai and Wang Xiyu had already booked their spots in the next stage.

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