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Heather Watson (GB) loses 6-1 6-1 to Sorana Cirstea on Court 13
Ana Ivanovic beats Alison Riske 6-3 6-0 on Arthur Ashe
Eugenie Bouchard through after beating Olga Govortsova 6-2 6-1
John Isner beats fellow countryman Marcos Giron 7-6(5) 6-2 7-6(2)
Live coverage of the US Open will continue on BBC Radio 5 live sports extra until about 23:00 BST, but our live text commentary must come to an end, I'm afraid. We will return on Wednesday. Bye for now.
There are other matches to talk about at Flushing Meadows. Ana Ivanovic is blowing kisses to the crowd after a 6-3 6-0 win over Alison Riske, and Sam Stosur has secured a 6-1 6-4 win over Lauren Davies.
Image source, Getty Images
Image source, Getty ImagesDespite that 54-minute defeat, it has been a productive year for Heather Watson who has introduced a touch of aggression to her game and returned to the top 50 after a difficult 2013. But Cirstea had too many weighty punches for the Briton today. On that showing, it'll be some time before the Briton reaches the second week of a Grand Slam. Well, 2015 at least.
That was short and not so sweet. Watson's body language during the on-court interview gave the impression that the Briton wanted to disappear under a cloak of invisibility. Unfortunately, she had to face the music and admit that the better woman won.
Heather Watson on Sky Sports: "I just wasn't able to find my game because she didn't give me much time. It's another week, so I'll just look forward to next week now and the doubles. It can't get much worse so only moving up from here."
Russell Fuller
BBC tennis correspondent at Flushing Meadows
"It was a horror show from Watson in the second set. You cannot give Sorana Cirstea enough credit, she did not let up and Watson was not able to deal with the situation. Her game disintegrated in the second set. Her serve did not work for her at all. Eight double faults and to lose in 54 minutes is a big shock."
Watson, on the run, a flick of the wrist and the Briton bamboozles her opponent with a crackerjack of a forehand. Is there more of that on the menu? Nope. Watson collapses like a soufflé. Cirstea still ahead at 15-30 and, without much effort at all, she collects double match points thanks to a Watson double fault. A marvellous crosscourt winner from Cirstea and the Briton is out after just 54 minutes on the court.
Image source, Getty ImagesRussell Fuller
BBC tennis correspondent at Flushing Meadows
"We were optimistic that Watson's steady progress up the rankings would continue, but Cirstea in the first set was magnificent with venomous hitting. A top five player would not play as well as that. Watson should not be too downhearted with the first set, but under pressure her game has deserted her in the second set."
A painful watch for Watson fans as the Briton is still unable to find the target. "Mother tennis can be so cruel," says Wayne Bryan in the BBC Radio 5 live sports extra commentary box.
With less than an hour played, Heather Watson - who had high hopes of reaching the second round - must serve to stay in the match.
Image source, Getty ImagesJohn McEnerney:, external This is going to be over soon unless HW gets her act together. SC is all over her like rash!
Laura Lambert:, external Don't doubt Watson's courage but has work to do. Needs to up her serve, and Cirstea's level will need to drop, to recover this.
A stooping Watson balloons a backhand long for 30-30 and the Briton needs to return to the aggressive game which earned her a place in the top 50 if she is to fight back from here.
Watson ends a lengthy rally with an overcooked forehand. To deuce we go. The forehand is Watson's enemy and so is her second serve - the 22-year-old winning only 14% of points on her second serve. Break point for Cirstea. The lights are flickering. A Watson backhand into the tape. Lights go out.
Watson performing like an out-of-control hosepipe, spraying groundstrokes here, there and everywhere. The match could be over before the Briton gains control of her racquet. She ends the game by going long. An easy hold for Cirstea.
BBC Radio 5 live sports extra
Wayne Bryan: "I don't like to coach too much from the commentary booth, but Heather serves too many ball in the net. The court is a long skinny rectangle and, if anything, the more you serve long, the better. She is playing well enough on the ground, but the serve is letting her down, both in terms of percentages and doubles."
Watson opens with a double fault and that sets the tone for the next few minutes as the 22-year-old concedes three break points and just as we were thinking momentum was with the Brit, she coughs up another double fault.
BBC Radio 5 live sports extra
Wayne Bryan: "Wow. Heather back to the haven of 1-1. That is an unbelievable, gutsy comeback because at 0-2 she was on her way out."
At 15-30, Watson has a sniff. The Briton crouches and blows at her fingertips at the baseline, as if to suggest she's prepared and ready for a showdown.
But Cirstea moves her opponent from side to side until Watson nets. Worry not, though, because Cirstea is fallible. A backhand into the tape - and Watson has a break back point! What has Watson got? Gravel for guts because she goes toe-to-toe with Cirstea and waits for her rival to crumble, the Romanian netting to gift Watson the break.
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Wayne Bryan: "Heather only has 50 per cent of her first serves going in. That won't do, especially against a big server like Sorana."
It's time for Heather Watson fans to hide beneath the covers. The Briton's serve is faltering - only 50% have found the target - and she presents her opponent with two break points, throwing in the towel with a clumsy netted backhand. A horror of an opening game.
Piers Newbery
BBC Sport at Flushing Meadows
Watson looks a bit stunned by this, it's been a terrific start from the previously out of form Cirstea, hammering down aces and clipping the lines. A bit of cloud cover gives brief respite from the sun, Watson could do with a lull at the other side of the net.
BBC Radio 5 live sports extra
Wayne Bryan, father and coach of the Bryan brothers: "At 1-2 both girls looked strong, but one double fault from Heather cost her a service game and Sorana was off to the races. She will play better in the second set and it should be a lot tighter."