WATCH: McDonald edged into his first ATP final at the Citi Open on Saturday, defeating Kei Nishikori in straight sets.

Mackenzie McDonald's first ATP final is a big deal, even if he's staying calm about it.

McDonald, 26, defeated Kei Nishikori to reach the Citi Open final in Washington, D.C., the deepest run he's had at an ATP event.

"It means a lot. I'm trying to downplay, or I guess downplay a little bit, try to keep my cool. I guess that's what's really helping me, not make the moments too big, getting too high or too low, staying focused," he told press from Washington, a 500-level event.

It's even more special for McDonald following surgery for a torn hamstring in 2019—he couldn't walk for three weeks and was off the tour for months, but says the hard work has helped him.

"It was tough, and I feel like it's come to it this week. I feel like I put it all together a little bit this week," he noted.

"It was really rough. I had no idea what to expect. I didn't know. I was away from family. I couldn't walk and drive myself. I had [an] apartment on the third floor and no elevator."

He spent most of 2020 coming back. "That first three months I was playing pretty bad tennis but I was healthy again," he said. "And then as soon as tennis started again, was a little bit lucky, had some [protected ranking events]. Hired my own coach. Put in a really good offseason and I was ready for the year."

McDonald got off to a good start, reaching the fourth round of the Australian Open -- that allowed him to keep his ranking up and compete in ATP events, and he's taken advantage of it.

"I didn't have, you know—if I didn't make fourth-round Aussie, honestly I would still be playing challengers. I wouldn't have the opportunity. I really dug deep. Did ten weeks in a row in Europe," he said. "Kind of about showing up each day."

Ranked No. 107, McDonald will break into the top 65 following Washington.