PHOENIX -- As he walked to the plate with his team trailing in the ninth inning Thursday night, D-backs designated hitter Seth Beer heard the fans chanting his name. He paused and remembered a lesson he learned in college and during his time in the Minor Leagues when he would hear chants like that.

"You have to learn how to deal with it because it can amp you up," Beer said. "I've had plenty of moments where I was trying to do too much in those situations and not had success."

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This was not one of those times, though, as Beer smacked a three-run home run to give the D-backs a 4-2 walk-off win over the Padres at Chase Field. Not only was it Opening Day, but Thursday marked National Beer Day on the many ¡°national day¡± calendars.

The coaching staff spent the spring drilling it into players¡¯ heads that they had to live in the moment, that they couldn't get bogged down by a bad at-bat or inning and instead had to push forward.

That advice came in handy when the offense was stymied throughout much of the night. Held hitless by Yu Darvish for six innings and scoreless through eight, the D-backs were able to rally in the ninth when Padres closer Robert Suarez walked the first two hitters he faced and then hit Carson Kelly to load the bases.

San Diego manager Bob Melvin went to his bullpen for Craig Stammen, and Beer worked on relaxing himself at the plate after getting a scouting report from hitting coaches Joe Mather and Damian Easley.

They told him Stammen uses a two-seam fastball to keep the ball away against left-handed hitters like Beer so he should look to stay through the ball.

"For me, it was trying to live in the moment and try to cool myself off and collect myself in between pitches," Beer said. "Take some breaths in between pitches and go 'All right, just look to do your job. Don¡¯t try to or be anything more than the player you are.'"

The first pitch Stammen threw was a curveball that bounced away and let the runners move up a base, making the score 2-1. That also changed Beer's approach.

"It made my job easier as a hitter," said Beer. "I said, if I can get something to the outfield, we can score a run and tie this ballgame. Thankfully, I barreled it up a little better than what I was planning on trying to do to help score that run. I put a good swing on that pitch."

And on National Beer Day, Beer connected with a Stammen curveball and sent it over the fence in right, becoming the first rookie in AL/NL history to hit a walk-off home run while trailing on Opening Day.

"It was a surreal feeling," he said. "It's still a dream. It's still really hard to put into words. I just kind of blacked out."

Beer's voice was hoarse after the game, the result of screaming as he rounded the bases, delirious with joy.

At some point before he rounded third he remembered as a kid watching players hit walk-off homers and throwing their helmets in the air.

"Man, it's crazy," he said. "I was like, 'I think I've got to just take my helmet off and throw it because that's what those guys did when I was watching as a kid.' So for me it was almost like living a dream. Just had to make sure it didn't come back down and hit me on the head. So I just kind of threw it, looked over and was like, 'All right, I'm good.'"

It's always easy to read too much into the result, good or bad, from Opening Day. It's just one of 162 games, after all, but it certainly had to encourage the coaching staff to see their message -- grinding until the last out -- play out like it did.

"That¡¯s what it¡¯s all about -- not giving in," first baseman Christian Walker said. "Holding your ground. It didn¡¯t start the way we wanted, but sometimes that¡¯s just somebody else doing their job. It¡¯s just a matter of plugging away, not giving away at-bats. Trying to make every swing count, all the way down to the last one. We didn¡¯t give up any outs and made it count at the end."