NEW YORK (AFP) — Serena Williams dramatically extended her iconic career on Wednesday with a never-say-die, three-set victory over world No. 2 Anett Kontaveit at the US Open.

The 40-year-old, 23-time Grand Slam title winner triumphed 7-6 (7/4), 2-6, 6-2 in front of a raucous, partisan Arthur Ashe Stadium Court crowd to reach the third round of a tournament she has won six times.

Having declared that she was already "evolving away from tennis" after a 27-year career, Williams' force of will ensured that the retirement party was put on hold for a little longer.

"There's no rush," said Serena on court when reminded that she had declared herself to be in the closing stages of her career.

"There's still a little left in me so we'll see. I'm a pretty good player. I love a challenge."

"I'm just Serena, you know. Honestly after I lost the second set I thought 'oh my goodness, I've got to give my best effort because this could be it."

She added: "I'm just looking at it as a bonus. I don't have anything to prove. I have absolutely nothing to lose. I've had an 'X' on my back since 1999."

The American arrived on court with the stadium announcer proudly introducing her as "the greatest of all time" while Kontaveit waited patiently at her chair.

Organizers, who laid on a spectacular welcome and post-match celebration for the American at her emotional first round win against Danka Kovinic on Monday, opted for a low-key party this time.

Golf superstar Tiger Woods watched from the Williams' player box while Emmy award winning actress Zendaya also boosted the A-list of invitees from the Arthur Ashe Stadium stands.

Only a repeat of rapper Queen Latifah's high-octane tribute to Williams delayed the start.

Kontaveit, whose Grand Slam career has yielded just one quarterfinal appearance, served a love game to get the contest underway but Williams was quickly level.

The 26-year-old Estonian fought off two break points in the third game but was then unable to convert one of her own in the fourth game.

Kontaveit saved four break points in the seventh game, each success greeted with muted, polite applause from the partisan crowd.

Former world No. 1 Williams, now ranked at a lowly 609, had the crowd on their feet when she converted the sixth break point for a 5-4 lead.

Her legion of passionate fans were quickly sitting down again when she handed the break straight back on a double fault.

Williams, however, played a composed tiebreak to take the opener after 63 minutes courtesy of a fifth ace.

To her credit, Kontaveit hit straight back, stretching to a double break for 3-0 before Williams retrieved one.

It was a brief respite as the Estonian broke again for a 4-1 lead on her way to leveling the tie.
Williams was ahead for 2-0 in the decider but then saw a 40-0 lead slip away as Kontaveit hit back.
The Estonian dropped serve again as Williams went to 3-1 and then 4-1 with a solid hold.
Victory was in sight at 5-2 with Williams winning a
19-shot rally.
It was all too much for Kontaveit who was broken to love with the match secured with a backhand winner.
Williams next faces Australia's Ajla Tomljanovic for a place in the Last 16.