Johanna Konta admits she simply ran out of steam at the US Open after her shock defeat to Latvia’s Anastasija Sevastova.
Konta was well below par in Arthur Ashe Stadium and she paid the price as world number 48 Sevastova won 6-4 7-5.
Since Wimbledon, Konta has played five tournaments, travelling to Stanford, Montreal, Rio for the Olympics and Cincinnati, before finally heading to New York.
The 25-year-old suffered an on-court collapse during her second-round victory at Flushing Meadows and, after losing to Sevastova, indicated she may not have fully recovered.
“I’m sure there are some remnants of it but it’s not the reason I lost today,” Konta said.
“I think also what happened a few days ago, it’s an accumulation of things. I have played a lot of tennis, especially in this space of time.
“I think it was just managing my energy levels today and managing what I had left in the tank and really maximising that.
“I felt I did that and unfortunately it wasn’t enough to play the kind of tennis I wanted to play.”
Konta showed glimpses of her best but could never sustain it long enough to gather any momentum.
The world number 14 was down 3-0 in the first set before levelling at 3-3, and trailed 4-1 in the second only to fight back to 5-5. On both occasions, she dipped at the crucial moment.
Overall, Konta made 34 unforced errors, more than five times the six she made in the previous round. Her serve, perhaps the Briton’s greatest weapon, was broken seven times.
“My opponent played an overall more solid match than I did,” Konta said.
“I’m really happy with how I was able to come back from 3-0 down. I thought I did a good job getting myself back into the match. It wasn’t easy.
“I didn’t play the tennis level that I maybe would have liked to have played, but I competed the best I could.
“It was a combination of things. I think I needed to perhaps be a little more offensive in certain parts and also be able to just move a bit better.
“I used what I had today and unfortunately it just wasn’t good enough to get me through.”
Sevastova’s remarkable run continues after she gave up tennis three years ago, fed up with injuries and poor form, to take up a course in management.
The Latvian returned in January 2015 and after seeing off French Open champion Garbine Muguruza here in round two, she has now upset Konta, ranked 34 places above her.
She next faces 2014 US Open finalist Caroline Wozniacki in the quarter-finals.
“I think I’m playing better in my second career,” Sevastova said.
“I’m handling pressure sometimes better than before. I still cannot believe it. Mentally I’m spent. Totally spent. But it’s amazing.”