PEORIA, Ariz. -- For all the “best shape of his life” clichés that tend to crop up during Spring Training, Marco Gonzales notably stands out.

“New prospect,” the Mariners’ longest-tenured player has said with a smirk to anyone who notices.

At least based on first impressions, though, there’s validity to his quip. Gonzales turned 31 last week, but after shaving 20 pounds from his frame and trimming the long locks from his brim, he looks more like the Gonzaga Bulldog from yesteryear and not the frustrated veteran who went off into the winter at arguably the lowest point in his career.

If it seems odd for Seattle’s stalwart to have been in such a rut after being the only player from before the club’s rebuild to remain when the team finally ended its playoff drought, it’s because he was on the sidelines once the Mariners finally broke through -- left off the postseason roster against Toronto and Houston.

“Disappointed. Bittersweet,” Gonzales said Saturday after the Mariners’ 5-1 loss to the Angels, his Cactus League debut. “I'm still trying to be there for the guys, but disappointed that I couldn't contribute and put spikes on. But I still tried to be there as a teammate, just trying to cheer on my friends. These are my best friends in this room.

“It's hard to be selfish and think I want to be on the team, but it's disappointing. I've thought about that moment since the moment I got here, what it'd be like to pitch in the playoffs, so not getting that chance, it hurts. It stings. It led to a lot of dark days this offseason, working through a lot, and so I guess that's what's led me to now, trying to re-prove myself here and trying to re-establish myself as an impact starter.”

The decision seemed inevitable after the Mariners acquired Luis Castillo at the Trade Deadline to round out a starting staff with Robbie Ray, Logan Gilbert, George Kirby and Gonzales, who the Mariners kept in the rotation as the No. 5 starter over Chris Flexen. But because the postseason’s first two rounds are shorter, teams typically only need three starters, maybe four. For example, Kirby did not start in the Wild Card Series and instead pitched in relief, as did Ray in the ALDS.

The decision to leave Gonzales off the postseason roster wasn’t personal, but rather, about Seattle’s personnel -- yet that didn’t make it sting any less.

“I understand where he's coming from and his frustration, having been such a big part and allowing us to get there,” Mariners manager Scott Servais said. “But in a short series, you go with the guys that are hottest and that's what we did.”

Added Gonzales: “I'm not one of our top three starters, and I understand that. So I can look at myself in the mirror and be honest with myself, and understand if that's what's best for the team.”

Over 32 starts last year, Gonzales had a 4.13 ERA and a 90 ERA+ (league average is 100) over 183 innings, good for 0.1 wins above replacement, per FanGraphs. That performance came in below his 3.5 in 2018 and career-high 3.6 in ‘19. Opposing hitters slashed .271/.322/.457 (.779 OPS) against him, with 38.1% of the 194 hits he allowed going for extra bases, owing at least in part to the fact that he ranked in the 20th percentile in quality of contact (xERA and xwOBA), according to Statcast.

There were big moments -- a few dominant outings against the Astros and the “I’m not sexy” hoot in Toronto -- but they were outnumbered by inconsistencies. So after the Mariners were eliminated, Gonzales worked to turn his frustration into motivation. It began with “a lot of dark days,” led to a lot of “angry workouts” and culminated with him “doing everything I can to not feel that way again.”

All that conditioning still couldn’t prevent the natural -- and annual -- feeling of being “gassed” in his spring debut, his first true ramp-up. He pitched a 1-2-3 first inning with three groundouts to shortstop, but then surrendered four runs on five hits in the second.

A month from now, Gonzales will embark on a comeback tour of sorts. He has always pitched with a chip on his shoulder, and he’ll lean on it in 2023 more than ever.

“It might even be a little bit of a bigger chip now. ... One thing that I've complimented him on is he's been a pro,” Servais said. “He's not let it affect him. It might have been hurting inside that he wasn't out there competing, but you never knew it on the outside. And I said that's a credit to him and being a real professional.”