SAN DIEGO -- What was billed as a pitchers’ duel turned into a battle of the bats Thursday night at Petco Park.

By the end of the Nationals’ 9-8 walk-off loss to the Padres, the showdown between right-handers Max Scherzer and Yu Darvish was overshadowed by an offensive spectacular.

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The Nats chased Darvish after only three frames. Scherzer didn’t last that much longer, exiting after 91 pitches in 3 2/3 innings. For both, it marked the shortest, non-injury-related starts of their seasons.

“Uncharacteristic,” manager Dave Martinez said. “I’ve never seen him like that. Just a tough fourth inning for him.”

The Nationals jumped out with three first-inning runs against Darvish, who had allowed a total of four first-inning runs all season. They plated eight across the first four frames, powered by two homers from Trea Turner in his eighth multihomer game of his career (third of the season).

The offense looked like a continuation from Wednesday -- a 15-5 blowout win.

“When he first got out there, I thought, ‘Man, this is going to be a good night,” Martinez said. “We come out, we score early, score often. We’ve got Max on the mound, and the way he was throwing the first three innings was really, really good. Just the wheels fell off there in the fourth inning.”

After Scherzer kept the Padres off the board for three innings, trouble brewed.

Scherzer allowed a monster home run to Fernando Tatis Jr. to open the frame. He fanned Jake Cronenworth, but then hit Manny Machado, allowed a single by Trent Grisham, hit Eric Hosmer and walked Wil Myers to plate a run. A strikeout against Victor Caratini brought reliever Daniel Camarena -- called up from Triple-A earlier in the day -- to the plate with two outs for his second big league at-bat.

In an unexpected turn of events, Camarena belted a grand slam off Scherzer. It was the first home run Scherzer has allowed to another pitcher in his acclaimed 14-year career.

Shortly after the game, Scherzer (seven runs, five hits, seven strikeouts) had absorbed the entirety of the inning and how he got to Camarena’s at-bat, not just the result of it.

“Just ran into a buzz saw there in the fourth,” Scherzer said. “I know a lot of attention’s going to be made to the grand slam, and rightfully so. But for me, the way I process that inning is [that] 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. So for me, that’s what I reflect upon and how I can pitch better in those situations.”

It was the first time a National League or American League pitcher had a grand slam for his first career hit since Bill Duggleby of the Phillies in 1898.

"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. Just 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."

With the game tied, 8-8, in the ninth, lefty reliever Sam Clay looked to send it to extra innings.

(Martinez said he would have called on Brad Hand for a save situation if the Nats had the lead.)

Down to the final out of the inning, the rookie Clay allowed a walk-off single by Grisham as the Nats dropped the series finale and departed San Diego with a four-game split.

“For me, I want to be able to get outs in those situations so I can pitch deeper in the game and save the ‘pen,” Scherzer said. “It’s not a good feeling when the ’pen’s been getting used to not pitch deep into a game in that situation.”

Scherzer entered Thursday with an extra day of rest for his final start before the All-Star break. He also had the momentum of holding opponents to one run or fewer in his last five outings. His approach before his next outing: “Just turn the page and move on.”

“That’s the funny thing about this game,” Scherzer said. “You can think that you have something working and you have flow and everything. Then shows you how quickly it can turn. This game can snap in a heartbeat like that. When you’re up 8-0, there’s never just a free out, a free at-bat, like you can throttle down and just pitch. No, that’s never the case in the Major Leagues.

“I’m not saying that happened tonight, but when you don’t put away batters in specific situations, when I’m in my kill counts, bad things happen.”