LOS ANGELES -- With each successive ball outside the strike zone, a sold-out Dodger Stadium crowd grew louder, eager to throw Kodai Senga off his game. In National League Championship Series Game 1, Senga may not have needed the help.

Making just his third outing of the year in one of the Mets’ most important games in recent memory on Sunday, Senga walked four batters, threw a wild pitch, committed a pitch clock violation, served up two hits, recorded only four outs and allowed the first three runs in a 9-0 loss to the Dodgers.

“He was off,” Mets manager Carlos Mendoza said. “He didn’t have it.”

From the jump, Senga struggled, throwing 13 of his first 16 pitches outside the strike zone while topping out at 94.5 mph -- two and a half ticks lower than he did in NLDS Game 1 against the Phillies on Oct. 5. His average fastball velocity was nearly a full mile per hour slower on Sunday, and he didn’t throw his sweeper at all -- problems he attributed largely to mechanical issues.

In nearly every one of his answers during a postgame press conference, Senga referred to his mechanics, though he declined to dig into specifics. Such issues are nothing new for the right-hander, who delayed returns from the injured list multiple times this season because he didn’t feel comfortable with various aspects of his mechanics.

“I thought you could see clearly that Senga just didn’t have his ‘A’ stuff tonight,” Dodgers manager Dave Roberts said. “The split was non-competitive. He didn’t use his sweeper. And then he was just relying on the cutter, working behind hitters, walking guys.”

The Mets had chosen Senga to start Game 1 over other well-rested options, including their best second-half pitcher, Sean Manaea. They did so because of his pedigree, yes, but also because they liked the way Senga looked in a two-inning sample during the NL Division Series. They did so without much other evidence that Senga could still resemble the pitcher who had produced a 2.98 ERA over 29 starts as a rookie in 2023. And they did so without a well-strung safety net behind him.

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In removing Senga after only four outs, the Mets also burned David Peterson, who had recently emerged as their top late-game weapon against left-handed hitters. Peterson wound up throwing 40 pitches, which will render him unavailable at least for Game 2. But the relatively heavy workload could set Peterson up to replace Senga as the Mets’ Game 5 starter, should they decide to go that route. And should they render a Game 5 necessary.

Asked late Sunday about his pitching plans, Mendoza declined to name Senga his Game 5 starter, but he did offer optimism about having Peterson available as soon as Game 3. In the interim, Mendoza and pitching coach Jeremy Hefner will monitor how Senga bounces back from this start. They’ll also weigh the pros and cons of using Peterson in short relief versus having him available to replace Senga in a potential Game 5.

“I don’t think it’s tricky,” Peterson said of the uncertainty. “We’ll have a conversation about it. We’ll talk about where I was pitch-wise and what they see for me the next couple of days, and we’ll formulate a game plan from there.”

A more pressing issue for the Mets will be winning Monday’s game, which would make the entire picture look rosier. Although the Mets only trail this best-of-seven series, 1-0, they played one of their sloppiest games in recent memory to drop Game 1. It took their hitters until the fifth inning to record a hit off Dodgers starter Jack Flaherty. Moments after they did, Jesse Winker made multiple baserunning mistakes on the same play to squelch that rally.

But Senga, who missed all but one start during the regular season due to shoulder, triceps and calf injuries, was the one who thrust the Mets in a deep early hole.

“Today was just one of those days,” Mets shortstop Francisco Lindor said. “He didn’t have his best stuff, but he gave everything he had. That’s all you can ask from a guy who was ready, who was prepared, who looked like he was in a good spot.”

If nothing else, Senga said through an interpreter, he is 100 percent healthy, no longer dogged by the injuries that robbed him of most of this season.

“Obviously, I’m frustrated and disappointed,” he said. “But I need to keep making adjustments.”