In case, in the wake of miraculous 2017 seasons from Roger Federer and Rafael Nadal, tennis fans had forgotten that comebacks are not always immediate and can span a long and bumpy road, the Citi Open has served as a clear reminder these past two days.

Federer and Nadal split the four Grand Slam titles of the 2017 season after each took months off to deal with varying ailments. But Stan Wawrinka knows that Federer and Nadal are anomalies in tennis. Wawrinka’s comeback from a knee injury that required two operations last August hit another speed bump Tuesday at Rock Creek Park Tennis Center as American Donald Young knocked out the three-time Grand Slam champion, 6-4, 6-7 (7-5), 7-6 (7-3), on Stadium Court. Young advances to face No. 7 seed Kei Nishikori in the second round.

“It’s a tough loss, that’s for sure,” Wawrinka said. “It’s painful to lose in the first round here, especially 7-6 in the third. There were some positives, but I saw a lot of negatives. I was missing a lot, not feeling the way I wanted — I’m looking for confidence, for sure. It’s tough to not win a lot of matches. Then you start to think too much on the court.”

Luckier than Wawrinka was Andy Murray, the other former major title winner on the comeback trail in the Citi Open men’s draw. On Monday, Murray endured a three-hour rain delay to prevail in a hard-fought, three-set match over 23-year-old American Mackenzie McDonald.

It was Murray’s first hard-court win in more than a year, and it was not the glossy re-entry to competitive play Federer and Nadal drew up last year.

“People thought we would come back earlier because the year before, Roger and Rafa came back directly at the top,” Wawrinka said. “But at the end, in sport, you cannot compare any injury. We all have different problems, different injuries, and we’re all trying to be back at the top.”

Wawrinka watched Murray on Monday night — his match against Young was originally scheduled to be played after Murray’s victory but was pushed back because of rain — and was pleased to see him back and winning. But the Brit seemed much more mentally fit than the erratic Wawrinka did Tuesday.

The Swiss’s fitness was there, but his signature backhand was unreliable and stringing together games and points proved to be difficult. He now heads to play qualifiers at the tournament in Toronto — he requested a wild card but was not afforded one — with his ranking of No. 198 set to take a dip.

Wawrinka, who has won every Grand Slam tournament but Wimbledon, has pledged to be patient with himself.

“It’s a really long process. There are different steps during the last year — it’s been a year already. Right now, it’s getting back the little confidence, putting out the doubts you have in your game. . . . I feel I’m really close, but at the same time I’m really far,” he said.

“I know and I’m sure I will get where I want to be, but it’s tough, it’s a long process, and you have to accept.”

Young was also focused on gaining confidence heading into the Citi Open. The Atlanta-based 29-year-old entered Monday’s match with a record of 2-10 on the year and played qualifiers looking to make up for what has been a poor 2018.

In Washington, he has good memories to fall back on. This is Young’s 10th year competing in the Citi Open, and the crowd showed him plenty of love even as he grew frustrated with himself on court.

“I haven’t had a bunch of confidence this year. Closing matches is kind of a skill you get from winning, and I haven’t done that,” Young said. “I love it here. I love the tournament, the people, the workers. I know half the workers. That definitely helps when you’ve done well and you have those memories. You don’t have negative memories. You have good ones,. You have positive ones, and you focus on that and not the negative.”

Young, like Murray and Wawrinka, simply hasn’t felt like himself this year. He demurred when asked to compare the Wawrinka he faced Tuesday night with Wawrinka in his prime and instead offered sympathy for his opponent.

“It’s just where we are right now,” Young said.