Click audio icon at the top of this page for radio commentary (UK only)
LIVE: Serena Williams beats Anett Kontaveit 7-6 (7-4) 2-6 6-2 to reach third round
Victory prolongs American's farewell before impending retirement
LIVE: Briton Jack Draper faces Canadian sixth seed Felix Auger-Aliassime in second round
Earlier: Andy Murray beats Emilio Nava 5-7 6-3 6-1 6-0 to reach third round
Britain's Harriet Dart loses 6-4 6-0 to Hungary's Dalma Galfi
Britain's Joe Salisbury and American Rajeev Ram make winning start to their men's doubles title defence
Jonathan Jurejko
BBC Sport at Flushing Meadows
More drama! Kontaveit saves break point with a forehand winner which takes the tiniest slither of the line.
The American fans boo because they think it is out. It isn't.
Williams quickly wags her finger to tell the crowd it shouldn't be argued and quickly diffuses the situation.
Class touch.
Williams 7-6 (7-4) 2-6 1-0 Kontaveit*
Oh my word! By the tiniest mark, Kontaveit catches the line as she digs out a winner to once again return to deuce.
The crowd don't like it but Williams wags her finger in response to let them know that's not on.
Williams 7-6 (7-4) 2-6 1-0 Kontaveit*
Serena Williams can't take her first opportunity, dropping short into the net.
She'll get another chance though! The crowd celebrate as Kontaveit lashes a forehand wide of the mark.
Williams 7-6 (7-4) 2-6 1-0 Kontaveit*
No panic from Kontaveit, who claws her way back to 30-30.
But a miss hands Serena Williams break point! Big moment.
Williams 7-6 (7-4) 2-6 1-0 Kontaveit*
This is a very good start for Serena Williams indeed.
She crashes a superb return down the line and Kontaveit then loops long. 0-30. The crowd have found their voice again.
*Draper 2-1 Auger-Aliassime
Jack Draper follows his break with a solid enough service game with a hold to 30.
The Brit then goes oh so close to going a double break up, seeing two break points go begging with Felix Auger-Alissiame's play littered with unforced errors.
This is a very good start from world number 53 Draper.
Williams 7-6 (7-4) 2-6 1-0 Kontaveit*
Laura Robson
Former British number one on BBC Radio 5 Live
It just looks like Kontaveit is chilling out and making sure that she stays loose. She has been in this position before - maybe not in this position with maybe the last set of career's career - but there is a lot of tennis to come.
Williams 7-6 (7-4) 2-6 1-0 Kontaveit*
That's a nice start to the set for Serena Williams, a couple of early winners putting her in charge before a booming serve completes a hold to 15.
Just what she needed.
*Williams 7-6 (7-4) 2-6 0-0 Kontaveit
Serena Williams left the court following the conclusion of the second set.
She's back, and we're ready for what should be a dramatic conclusion to this match - whatever the outcome.
Can Serena Williams keep her singles career going a little longer?
Jonathan Jurejko
BBC Sport at Flushing Meadows
Serena fans have come far and wide to see her final tournament - including Jennifer Chenier and Renicha Jones have flown over from Houston, Texas.
"Serena is the greatest of all time and I've always loved her. But this is my first time watching her!" beams Jennifer.
"When she announced she was retiring I told my best friend Renicha 'we're going!'
So what does 'The Woman, The Myth, The Legend' (check out the tee) mean to her?
"Growing up in Compton and what's she achieved through her being African-American and everyone hating on her and talking about other things besides just her skill is incredible.
"To see her win 23 Grand Slams, I'm praying she gets one more in this last tournament. That would A-MAZ-ING.
"I don't play tennis, the only reason I watch is because of Serena and Venus, seeing them do their thing."
Image source, BBC Sport*Williams 7-6 (7-4) 2-6 0-0 Kontaveit
Gigi Salmon
BBC Sport tennis commentator
A one-set shoot-out - will it be the final set of Serena Williams' career?
*Williams 7-6 (7-4) 2-6 0-0 Kontaveit
Laura Robson
Former British number one on BBC Radio 5 Live
It felt like Serena let that last set go - maybe just conserving some energy for set three.
*Williams 7-6 (7-4) 2-6 0-0 Kontaveit
Fifteen winners compared to three unforced errors for Kontaveit in that second set display.
The world number two has raised her level and Serena Williams is yet to find an answer after the high of taking that opener.
*Williams 7-6 (7-4) 2-6 0-0 Kontaveit
Don't go anywhere folks!
We are indeed going to a third set.
A final ace completes a fairly flawless second set for Anett Kontaveit as she comes roaring back to level the match in New York.
*Draper 1-0 Auger Aliassime
David Law
Commentator on BBC Radio 5 Live
Draper is going places in this sport quite quickly, and he is standing up to the Canadian. He looks like a man rather than a junior trying to transition into the tour.
Williams 7-6 (7-4) 2-5 Kontaveit*
Right then, it's over to Anett Kontaveit to serve for what has been a hugely impressive set and take us into a decider on Arthur Ashe.
*Draper 1-0 Auger Aliassime
Jack Draper breaks Felix Auger-Aliassime's serve in the opening game of their match.
Nothing spectacular from the Brit, just got the job done and the break on his second break point.
Williams 7-6 (7-4) 2-5 Kontaveit*
Laura Robson
Former British number one on BBC Radio 5 Live
The crowd are not doing a great job of getting behind Serena.
We can feel that her energy has dropped and she is getting a bit disheartened.
Williams 7-6 (7-4) 2-5 Kontaveit*
Serena Williams does what she needs to, sealing a fine love hold with a cracking ace down the middle.
*Williams 7-6 (7-4) 1-5 Kontaveit
No mistakes from Kontaveit in this service game.
She eases into a 5-1 lead with a terrific backhand down the line.