Sitting on an 0-2 count in a scoreless tie in the bottom of the 10th inning, the first baseman smacked a changeup from Royals right-hander Yasuhiko Yabuta (1-2) into the right-field seats, and the Diamondbacks walked off with a 1-0 victory in the series opener.
"That's my first big league walk-off home run," Tracy said. "Now that it's out, I don't think there's any better feeling in baseball than winning a game with a walk-off home run, especially with what I've been through trying to get back here.
"With two strikes, you can't really sit solely on that changeup. I was kind of sitting in between and trying to fight the fastball the other way, and if he threw me the changeup, just try to put it in play. I happened to put it on the barrel at the right trajectory and I hit it out of the ballpark."
It was Tracy's third home run since coming back from knee surgery in March. The shot ended an unusual version of a scoreless tie. The two teams left a combined 21 runners on base and had 12 walks combined, seven by Royals starter Zack Greinke, who threw seven innings.
D-backs starter Doug Davis had similar success in his seven innings, allowing 10 of the 30 batters he faced to get on base.
"That's me," Davis said. "It seems like I always get runners on and am able to make a pitch to get out of the inning."
The two teams also went a combined 0-for-13 with runners in scoring position.
Billy Buckner (1-0), who was making his D-backs debut after Max Scherzer was optioned to Triple-A Tucson, picked up the win against his former team. Buckner was recalled to give the bullpen a fresh arm after it had pitched 16 2/3 innings in New York.
D-backs manager Bob Melvin said he would have sent Buckner out for the 11th inning if it came down to it, even though Buckner threw eight innings in a start in Tucson just three days ago.
It was the D-backs third consecutive extra-innings affair, setting a new franchise record. The D-backs are 2-1 in that span.
"As long as we're coming out on top, that's all that really matters," Davis said. "We've been battling for the last month or so. We've just got to keep battling. These guys are working hard and it shows."
Tracy also had a stellar defensive play in the top half of the 10th inning. After umpires ruled that right fielder Justin Upton trapped a fly ball off the bat of Mark Grudzielanek with one out, Tracy snared a hard grounder from Alex Gordon, tagged first base and threw down to second for the double play that ended the inning.
Still, the talk after the game was about Tracy's homer.
"Typically 0-0 games like that, toward the end, a lot of times it takes a homer," Melvin said. "Everybody's trying to hit one, it seems like. He hit a changeup, got a good piece of it, and we'll take it.
"The farther these things go along, the more you tighten up. You want to be the hero. ... That's a home run that makes you feel like you're back and a part of it. It obviously was the big at-bat in the win. I know he'll go home with a smile on his face tonight. It was a good day for Trace."
Tracy is just happy to get back to making solid contributions after missing nearly an entire season with the knee injury. He may create quite the positional logjam once outfielder Eric Byrnes returns from the disabled list, which could happen this homestand. Regular first baseman Conor Jackson got his second start in left field.
"It's been about a year since I've played ball," Tracy said. "You go through your ups and downs trying to get everything back to where it was and trying to get your body feeling all right. I'm starting to feel like my knees are feeling good and I'm starting to feel 100 percent out here."
Mike Ritter is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.