US Open champion Emma Raducanu said she was still coming to terms with the fast pace of life on tour but vowed to brush aside her disappointing loss in the Transylvania Open on Friday and come back stronger.
Ukrainian Marta Kostyuk defeated the misfiring 18-year-old 6-2 6-1 in under an hour at the WTA 250 event in Cluj-Napoca, with the Brit committing 41 unforced errors during the contest.
"I wasn't physically feeling 100 per cent. I was quite tired and lethargic today. Sometimes you just have those days where you don't feel your best," Raducanu told reporters. "I knew from the morning, I knew from practice.
"I wanted to go out there on the court and try my best and see how it was going to go, maybe it would go better. But I just couldn't get it going today unfortunately.
"It's just disappointing that you have these days. It's not a nice feeling to have, but I just need to move on from it and brush it off. And then I'll be back in another tournament soon."
Raducanu stunningly won the Flushing Meadows title in September as a qualifier and after the Grand Slam announced that she would no longer be working with former Davis Cup player Andrew Richardson.
The Brit said "things are looking up, so it's going in a good direction" with her search for a new coach.
Raducanu won her first two matches on the WTA tour this week and is scheduled to play her last tournament of the season at the Upper Austria Ladies Linz from November 6-12.
"I think it's just the last six months," she said. "It's been a lot of learnings and I've experienced a lot in the last six months with not so much gaps.
"I'm just adapting to the fast-paced life of the tour and obviously still very new to it, so it's still going to take me some time to adjust.
"After Linz I'll probably have a week off just to reset and (be) mentally and physically fresh for the tough preseason. It's going to be my first one and from what I've heard, it's a very difficult four weeks physically."