SAN DIEGO -- One pitch into Monday's long-awaited showdown with the Dodgers, the Padres found themselves trailing by a run. Joc Pederson unloaded on a Chris Paddack fastball and sent it into the left-center-field seats. The seven-time reigning division champions -- the very team the Padres have spent a decade chasing in the National League West -- had delivered the first punch. Again.

But the Padres have resolved that they’re a different team this year. So moments after Pederson touched home plate, there was Paddack, heels on the rubber, glove in front of his face, practically begging Max Muncy to hurry up and get in the box. The Padres wanted a chance to punch back. This time, they would.

Trent Grisham, Wil Myers and Fernando Tatis Jr. all homered in a back-and-forth 5-4 victory over their Southern California rivals on Monday night at Petco Park.

• Box score

“Tonight was a dogfight,” said Paddack, who pitched six innings of three-run ball. “We got the bone.”

Twice, a Paddack mistake put the Padres behind by a run. Both times, the San Diego offense roared back. Grisham launched a 436-foot homer off Walker Buehler in the bottom of the first inning, an emphatic response to Pederson’s leadoff shot. Then, after Will Smith’s two-run double put the Dodgers ahead in the fifth, Tatis hit an oppo bomb off Buehler with two outs in the bottom of the frame.

Paddack, meanwhile, locked himself back in immediately. He used his curveball perhaps more effectively than he ever has, even though his fastball and changeup were working, too. Paddack threw 14 breaking pitches -- including a bender that struck out reigning NL MVP Cody Bellinger with a weak half-swing in the fourth inning.

“One run, I knew, wasn’t going to beat us tonight,” Paddack said. “It’s in my hands, I’ve got to continue to compete, continue to show these boys I’m going to go out there and grind for ‘em. It’s always a good feeling when your offense picks you up.”

It was a stark contrast to the way the San Diego offense has flailed against Buehler in the past. The right-hander was 4-0 with a 0.64 ERA in four career starts against the Padres. Perhaps it’s symbolic of the changes they made during the offseason. They acquired Grisham, for instance, and suddenly he looks like a mainstay in center field. He went 2-for-3 with a walk on Monday, and through 12 games, he’s hitting .293/.396/.683.

The Padres chased Buehler after five innings and went to work on a Dodgers bullpen that entered Monday with the lowest ERA in the Majors. Jake Cronenworth singled home Manny Machado to put San Diego on top, and Austin Hedges added another RBI single, his first hit of the season, to make it 5-3.

• Notes: Machado on shifts; Abraham Almonte called up

From there, the Padres finally got a mostly stress-free night from their bullpen. Emilio Pagán and Drew Pomeranz pitched a scoreless inning apiece before Bellinger took Kirby Yates deep to start the ninth. But the Padres’ closer rebounded with three straight strikeouts to end the game. After allowing multiple runs in each of his last two outings, Yates finally looked like, well, Kirby Yates.

“That’s a little bit of what we’d envisioned from the get-go,” said Padres manager Jayce Tingler. “To see it tonight, to see it against a really, really good team, it felt good, and hopefully we can build some confidence and build some momentum and keep it going back there.”

The Padres could have -- and probably should have -- busted the game open in the seventh inning. But a pair of baserunning blunders cost them. Grisham was nailed trying to stretch a single into a double for the first out. Then, after Machado lined out to right field, Tatis got caught in a rundown between third and home.

“We got a little too over-excited,” Tingler said. “Besides those couple blemishes, which are things we can clean up, I thought that was one of our better-played games of the year.”

And it came in a high-intensity setting -- as evidenced by the postscript to that rundown. Tatis, as he is wont to do, did his best to escape multiple tags. This time, his aggressiveness only resulted in an out, and a collision with Smith.

Justin Turner, who delivered the throw to Smith, was none too pleased with the contact on his catcher. Turner had a few choice words for Tatis, who appeared to chirp back. But both sides retreated to their dugouts, and nothing more came of it.

Just a high-stakes baseball game between two division rivals.

“What y'all saw tonight was playoff baseball,” Paddack said. “It was back and forth, and the energy level, even without the fans, was tremendous.”

“I’ve never played Major League playoff baseball, but if I had to guess, that’s what it’s like,” said Cronenworth.

Playoff baseball -- been a while since the Padres experienced that.

They know their path in the NL West goes through the Dodgers, and they started 2020 by punching back.