NEW YORK (AFP) - Sloane Stephens, her dream of a US Open title defense in tatters, was looking ahead to the WTA's Asian swing as a chance to regroup and renew her pursuit of the No. 1 world ranking.

"Obviously from three there's only two more spots to go," she said before the Open. "That's exciting. It's something new."

And it's a challenge that doesn't end with her 6-2, 6-3 quarter-final loss to 19th-seeded Anastasija Sevastova on Tuesday (Sept 5).

Playing in punishing heat and humidity, with a sinus infection that has plagued her since the tournament began, Stephens shied away from excuses, saying she just didn't play well enough to win.

"I didn't play my best," she said.

"I wish I could have played better, but it just wasn't the day."

Stephens was an 83rd-ranked outsider when she roared to the title last year, cementing her return from an 11-month injury absence.

She insisted she still had plenty to be proud of.

"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, a lot to be proud of," she said.

"Obviously defending a title is very hard. 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."

After her maiden Grand Slam triumph Stephens didn't win another match in 2017.

Now she's aiming for a strong finish to the year.

"Considering last year after this tournament I shit the bed for like 10 tournaments in a row, I definitely don't have any points to defend," she said.

"I hope that I can go to Asia and win some more matches and hopefully make the year end and hopefully keep going as far as I can."