Naomi Osaka played down the impact of a knee injury that affected her as she exited the fourth-round to Belinda Bencic.
The defending champion went down 7-5 6-4 to Switzerland’s Bencic in the last 16 on Monday.
Osaka, 21, was broken late in the opening set and then again in the fifth game of the second at Flushing Meadows.
The Japanese player finished the match with a strapped knee and needed medical treatment in the second set as an injury picked up last month in Cincinnati hampered her efforts to get back into the match.
But she did not want to blame the defeat on the injury.
Osaka said: “She [Belinda] had a specific plan she wanted to execute.
“I don’t want to answer saying everything I did wrong. I want to think about it more positively.
“I hurt my knee in Cincinnati but it’s getting better. I don’t want to say that’s the reason I lost because I played three matches before this. I just had to take a painkiller.
“I have this feeling of sadness but I also feel like I have learnt so much during this tournament.
“Of course i wanted to defend this tournament but the steps I have taken as a person have been much greater than I imagine.”
Osaka, who followed up her maiden grand slam at New York last year with the Australian Open title in January, was more upbeat after elimination at Flushing Meadows than when she crashed out of the French Open and Wimbledon earlier in the summer.
This is despite losing her world number one ranking, with French Open champion Ashleigh Barty of Australia setto return to the top spot.
“I feel I am more chilled and have grown and didn’t put so much weight on one match,” she said.
“The biggest lesson I have learned is not to take myself too seriously and to know there is always another tournament.
“I have learned over the summer that even if you play your best you are going to play someone else playing at their best.
“The level of tennis I was playing in Europe was not that great.”
Bencic, 22, will look ahead to her second appearance in the US Open quarter-finals having made the last eight in 2014.
She will now play Croatia’s Donna Vekic after the 23rd seed beat Germany’s 26th seed Julia Goerges 6-7 (5-7) 7-5 6-3 in a match that lasted two hours 42 minutes on Louis Armstrong Stadium.
“I was so excited to come on the court, the challenge cannot be bigger – Naomi Osaka is a great player and won the US Open last year,” said Bencic. “I had to be on top of my game and am really pleased with how I played.
“She has a lot of power, I was just trying to play it a little bit like chess, anticipate and make a tactic on the court.”
Osaka, who beat Serena Williams in last year’s final for her maiden Grand Slam title, started off badly as she lost her serve at the first opportunity and had to save two break points to avoid going 3-0 down.
She then fought back with a break before Bencic took the decisive break in the 11th game and then served out the set.
In the second set, an Osaka double fault gifted Bencic another break and the Swiss player took the final game of the match with a service game to love.
After winning the Australian Open in January for her second Grand Slam, Osaka became the world number one, a position she held until June before Barty took over.
Osaka returned to the top eight weeks later but Barty will become number one again, despite losing in the last 16 to China’s Qiang Wang on Sunday.