SAN DIEGO -- In a matchup of aces Thursday night, Padres rookie reliever Daniel Camarena stole the show.

With one of the most unlikely at-bats you could think of, the 28-year-old left-hander joined the Slam Diego ranks in incredible fashion. His fourth-inning grand slam off of Max Scherzer spurred the Padres to a 9-8 walk-off victory over the Nationals at Petco Park.

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The Padres trailed, 8-0, at one point in the fourth inning, and the Nats had a 98% win probability. That number was still at 94% when Camarena stepped to the plate with the Padres down by six runs.

“I still don't have a word for it,” Camarena said. “I'm still trying to find a word for my debut, and then this took it to a whole other level. In that AB, just trying to put the ball in play in that situation. Especially against Max, that's hard to do. I was just trying with everything that I had just to put a ball in play."

Camarena came into the game to pitch the top of the fourth inning after Padres ace Yu Darvish gave up a season-high six runs in three innings. After the Padres loaded the bases in the bottom half of the frame, Camarena connected on a 96.5 mph fastball from Scherzer that he sent 416 feet to right field for the two-out grand slam, pulling the Padres within two runs, at 8-6.

A native of the San Diego suburb of Bonita, Calif., Camarena was recalled from Triple-A El Paso earlier Thursday. Like fellow San Diegan and Padres' teammate Joe Musgrove, who threw the Padres first no-hitter in franchise history, Camarena made some history.

Camarena became the second pitcher in Padres history with a grand slam, joining Mike Corkins (Sept. 4, 1970). Camarena is also the first relief pitcher from any team to hit a grand slam since Don Robinson on Sept. 12, 1985, for the Pirates against the Cubs.

Camarena said having his family in the stands at Petco Park made the moment even more special.

“Family is everything to me,” he said. “We've been so tight-knit. I mean my older brother, we probably spent more time in the batting cage at home than we did practicing pitching. I still haven't even gotten the chance to see him, so I can't wait to give him a big hug and just share this moment.”

Collecting his first hit via a grand slam also made Camarena just the second pitcher to do so. The only other pitcher in National League or American League history to record his first hit via a grand slam was Bill Duggleby who went deep on April 21, 1898 with the Phillies, according to STATS.

It also was the first time Scherzer allowed a home run with a pitcher at the plate, much less a grand slam.

Camarena’s slam highlighted a comeback win for the Padres, which ended on Trent Grisham’s walk-off single in the ninth that brought home Tommy Pham.

The eight-run comeback tied the biggest comeback win in Padres history. On only two other occasions have the Padres fought back from eight-run deficits -- on June 10, 1974 against the Pirates and May 2, 1970 against the Giants.

“You can go all across the lineup card tonight, and everybody got in and is contributing,” Padres manager Jayce Tingler said. “… We're going to enjoy it, but we quickly got to turn the page.”

Fernando Tatis Jr. led off the bottom of the fourth inning with a 433-foot solo home run that led to a seven-run inning and broke the scoreless drought against Scherzer.

The Padres’ bats followed that up by loading the bases after Manny Machado and Eric Hosmer were hit by pitches and Grisham singled. Wil Myers drew a bases-loaded walk two batters before Camarena cleared the bases.

“I know a lot of attention’s going to be made to the grand slam, and rightfully so,” Scherzer said. “But for me, the way I process that inning is, I had two strikes on some other batters there. Specifically, I wasn’t able to get Machado out. I wasn’t able to get Hosmer out. I wasn’t able to get Wil Myers out. Those are the at-bats that extend the inning that provide that opportunity.”