Until the Mets bullpen blew it, Brandon Waddell’s Mets debut had all the pieces for a storybook ending in Queens.

The player made his entrance in the third inning, following the opener Huascar Brazobán, marking his first MLB appearance in nearly four years. This moment marked the pinnacle of his baseball journey that included stints with various teams such as the Cardinals, the Korea Baseball Organization, the Chinese Professional Baseball League, a return to the KBO’s Doosan Bears, and a start in 2025 with Triple-A Syracuse.

After an impressive debut, he left the game 4 ¹/₃ innings later to a standing ovation. At that point, he was on track to secure his first MLB win, having struck out four batters, allowed only three hits, and not conceded a run in the eventual 4-3 loss to the Diamondbacks at Citi Field on Wednesday.

“It was awesome,” Waddell said. “It’s good to be back.”

Waddell wanted to return to MLB to prove he could still pitch at this level, he said.

While pitching internationally, he learned to pitch aggressively and induce weak contact, and that translated into his outing Wednesday.

His performance established several milestones; he became the first Mets reliever and just the 15th Mets pitcher overall to pitch at least four innings in his team debut. Furthermore, it was noted as the longest appearance by a Mets reliever since Nelson Figueroa’s 4 ¹/₃ innings in 2009, according to the team’s records.

“You learn a lot of over there,” Waddell said. “You learn how to pitch. You learn how to use your stuff. So it’s just taking those lessons and refining things.

“As you go along in your career, pitches get better. Maybe adjust a couple things, but it’s really just trying to learn every time you’re out there.”

Eventually, with the Mets needing someone to take the bulk of the innings Wednesday, that all led to Citi Field, where Waddell mixed a four-seam fastball, a slider, a sweeper, a cutter and a changeup to keep the Diamondbacks off-balance.

They didn’t manage an extra-base hit against him.

His night ended when he struck out Josh Naylor on a slider to start the seventh, and as manager Carlos Mendoza took the ball and waited for Stanek to enter from the bullpen, that’s when the standing ovation began.

This could all be fleeting for Waddell.

At 30, he’s still searching for his first win, still searching for consistent chances on the sport’s ultimate stage that evaded him even earlier in his career with the Pirates, the Twins, the Orioles and the Cardinals — stops where he collectively logged 11 appearances after originally being a fifth-round pick in 2015.

But for one night, for one spot when the Mets needed an extra member of their rotation, he was “unbelievable,” Mendoza said.

“It’s something I definitely didn’t expect,” Waddell said of the standing ovation, “but you can feel it as a player. It means a lot to have that support and something that we always really cherish.”