WASHINGTON (AP) — Stan Wawrinka's surgically repaired left knee is just fine. What's missing now for the three-time major champion as he goes through a rough season is the self-belief that comes with success.

Wawrinka's latest quick exit came Tuesday night at the Citi Open, a 6-4, 6-7 (5), 7-6 (3) loss against 234th-ranked qualifier Donald Young of the U.S. in the first round of the hard-court tournament.

"I was missing a lot. Not feeling the way I wanted. I'm looking for confidence, for sure," said Wawrinka, who has been ranked No. 3 but is merely 198th at the moment on account of a 6-11 record in 2018 after two knee operations last year. "It's tough to not win a lot of matches. Then you start to think too much on the court."

This was Wawrinka's first match since bowing out of Wimbledon in the second round in early July; his ranking is so low that he needed a wild-card entry just to get into qualifying for his next event, in Toronto.

The only other time Wawrinka entered the U.S. Open tuneup in Washington, in 2010, he also lost his opener.

Right now, his issue is the doubt can creep up at key points in a match.

"I feel I'm really close but, at the same time, really far. The positive right now is that physically, I'm feeling good. Tennis-wise, I'm practicing well. I can put (in) a lot of work on the court," said Wawrinka, who has won the U.S. Open, Australian Open and French Open once apiece. "I know and I'm sure I will get where I want to be. It's just tough. It's a long process and you have to accept (it)."

He and Young, who came into the day with just a 2-10 record this year, were supposed to play Monday night. But because of rain delays and a lengthy match before theirs, they only made it onto the court to warm up at 1 a.m., and then a downpour arrived, so the contest was postponed.

Wawrinka got broken in the first game Tuesday by dumping a forehand into the net; that turned out to be the match's only break. Wawrinka then was two points from losing at 5-3 in the second-set tiebreaker. But a series of miscues by Young, including a double-fault at 5-4, sent them to a third set. This time, Young held on, and he'll face 2014 U.S. Open runner-up Kei Nishikori on Wednesday.

"Fought a lot of nerves there, but I'm happy the end result was a 'W,'" Young said. "Closing matches is kind of like a skill you get from winning and I haven't done that — but I was able to do that."

No. 1 seed and defending champion Alexander Zverev took the first set against Malek Jaziri 6-2 in the main stadium's final match when play was suspended for the night after 1 a.m. because of rain. They'll resume Wednesday.

In earlier action, local product Denis Kudla — who is staying at his parents' home in nearby Arlington, Virginia, this week — collected his first victory in seven attempts at the Citi Open, coming back to beat Lukas Lacko of Slovakia 6-7 (3), 6-1, 6-4.

"This is always a place that I've wanted to win and I've always struggled here. My record was pretty awful coming into today," said Kudla, who had been 0-4 in main-draw matches and 0-2 in qualifying at the tournament. "Today it just came together."

Marcos Baghdatis, the 2010 runner-up, advanced with a 6-3, 3-6, 6-2 victory over Benoit Paire, who drew boos from spectators after a racket-breaking tantrum. Vasek Pospisil, a finalist in 2014, lost to 19-year-old Alex de Minaur 6-7 (6), 6-2, 6-3.

Australian Open champion Caroline Wozniacki pulled out of the women's draw because of an injured right leg, while defending champion Ekaterina Makarova lost her first-round match to Ana Bogdan 7-6 (2), 6-3.

No. 2 seed Sloane Stephens, the reigning U.S. Open champion, moved into the second round with a 7-5, 6-4 victory over Bethanie Mattek-Sands.

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