|Venue: Flushing Meadows, New York Dates: 28 Aug-10 Sept|
|BBC coverage: Live radio and text commentary on selected matches every day.|
Britain's Johanna Konta said it was "tough to take" as she headed home from the US Open after just one day following defeat by Aleksandra Krunic.
The unseeded Serb won 4-6 6-3 6-4 against the seventh seed to cause the first major upset of the tournament.
Konta had been hoping to improve on previous semi-final appearances at Wimbledon and the Australian Open.
"It's definitely not an easy defeat to take - it was a close match," Konta told BBC Radio 5 live.
"It went to three sets and over two hours. I try to keep a very good perspective on how this sport works and that is there are no easy matches.
"First rounds are always tricky and difficult, regardless of the tournament but I guess especially in Slams, so I think that's for everybody, not just me.
"My opponent dealt with it and I competed until the very last ball, so I can't be too harsh on myself in that sense, but I've definitely got a lot to improve on, which is also a positive thing."
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Konta, 26, has enjoyed another terrific year, cementing her place inside the top 10, winning one of the biggest titles in the sport in Miami, and reaching the quarter-finals at the Australian Open and semi-finals at Wimbledon.
There was every reason to believe that she would reach similar heights at Flushing Meadows, on her favourite surface of hard courts, but she produced an erratic performance on day one.
After easing into a 4-1 lead, the Briton's serve deserted her and hovered around the 40% mark, allowing Krunic to take the initiative.
"Credit needs to be given where it's due and that's to how my opponent played," said Konta, who finished the match with 42 unforced errors.
"I felt that she raised her level of tennis consistently throughout the match, whereas I struggled to maintain that and fluctuated a little bit more.
"That's credit to her for playing as freely as she did."
Konta had arrived in New York with an outside chance of taking the world number one ranking, but she is now looking the other way and hanging on to a place in the top eight.
That would give her a place in the season-ending WTA Finals for the first time, after she narrowly missed out in 2016.
"The goal is to stay healthy, for one, and play a full season, but also to keep trying to get better.
"I think, if anything, today gives me a great opportunity to do just that, and I've got still a few tournaments left in the season, and if Singapore is in the cards for me, then I will take it and be very grateful.
"If not, I will take what comes my way."