Sloane Stephens revealed she had been struggling with a sinus infection prior to her US Open exit at the hands of Anastasija Sevastova, but she refused to blame the illness for the defeat.

Stephens was beaten 6-2 6-3 by the Latvian in their quarter-final clash, ending the American's defence of her maiden grand slam title.

The third seed struggled throughout on what is expected to be the hottest day of the US Open, failing to take her chances as Sevastova coped better with the challenging conditions.

But Stephens said afterwards that she had been feeling under the weather in the build-up to the match.

"I have been sick since, I don't know, since Monday," she told a news conference. "Bad sinus infection. Whatever. You've got to play.

"I have been playing well the last matches. It was just a tough day. I didn't play my best. I wish I could have played better, but it just wasn't the day."

Despite the illness, Stephens added: "I was excited to play, happy to get out there and compete.

"It was a bad day. I wish I could have played better. The better player won."

And while conceding that seeing the defence of her title come to an end was a huge disappointment, Stephens was relieved to make it as far as she did in the tournament.

Asked what positives she would take from her performances, the 25-year-old said: "That I could have s*** the bed in the first round, and that would have been really bad.

"So the fact that I made it to the quarter-finals and played some really good matches and I just competed as hard as I could, I mean, a lot to be proud of.

"And obviously defending a title is very hard, very difficult. If you were defending, you'd be playing the same exact people all over again, which I didn't. I made the most of it this week or the last 10 days, whatever it was.

"I can be proud of a lot of things that happened the last couple, the matches that I played, so I'm not going to dwell on it. Just keep building.

"There's four more tournaments left. I'm just going to try to play the rest of the season as hard as I can and hopefully have some more good results."