PHOENIX -- Monday afternoon's series opener went well for Rockies right-hander Peter Lambert, until the fourth-inning snowball.

The 4-2 decision was the Rockies’ 11th loss in 14 games, but Lambert accounted for himself well with the exception of the four straight hits that saw the D-backs score three runs in the fourth. That was more than enough for Arizona starter Merrill Kelly, who struck out a career-high 12 batters in seven-plus innings.

“It all came down to that fourth inning,” Lambert said. “It snowballed on me a little bit. It happened really fast. I should’ve taken a step back.”

At some point the Rockies (50-87) will do just that -- take a step back at the end of the season, which is looking increasingly like the first one of 100 losses in club history. But if Lambert keeps pitching as he has since he was finally healthy enough to rejoin the starting rotation, Colorado will see games like Monday as a step forward for the club.

Lambert held his stuff through 94 pitches, going six innings, while striking out five and giving up six hits.

It’s not just that Lambert is throwing, although being on the mound in and of itself is not to be taken for granted. He pitched minimally from his Tommy John surgery in July 2020 through last season. It’s that he is a competitive pitcher who is gaining savvy the more he is on the mound.

After Christian Walker’s leadoff single in the fourth, Lourdes Gurriel Jr. doubled, Gabriel Moreno singled and Jace Peterson doubled. After Walker’s hit, all the other hits were on breaking balls.

But with three runs in, a 4-0 deficit and no outs, Lambert retired the final nine hitters he faced -- four on strikeouts. Known for working away from hitters, Lambert began challenging at the top of the strike zone.

After the D-backs’ rally, Lambert fanned Corbin Carroll to end the fourth and Alek Thomas to start the fifth on high heaters. He used his willingness to go up in the zone to set up changeups to fan Tommy Pham in the fifth and Gurriel Jr. in the sixth.

“It was part of the game plan for sure,” Lambert said. “Especially in that fourth inning, we realized that they hit some offspeed pitches pretty well. In order to make those more effective, we had to use the fastball a little more.

“In a 4-1 game, you’re still in the game. Those are crucial innings, to make sure we don’t blow up our bullpen the first game of a series. That’s important, as well.”

When the Rockies reconvene for 2024, Germán Márquez and Antonio Senzatela will still be recovering from their Tommy John surgeries, while Kyle Freeland will be trying to rebound from an undesirable 2023 (which continues with Tuesday’s start against the D-backs). That’s every starter who has represented the club in a postseason game.

Lambert pitching like the second-round MLB Draft pick he was -- in 2015 out of San Dimas (Calif.) High School -- would give a pieced-together rotation a better chance to make noise with what is expected to be another year of building.

“We’ve talked so much about fastball command -- the essential for a starting pitcher,” Rockies manager Bud Black said. “He’s got to work his way through a lineup multiple times. And you’ve got to be able to command the fastball to both sides of the plate. You can’t locate just one side. Peter is really understanding and appreciating the fact that against lefties and righties, there’s an inside attack at the hands and down-and-away as well.”

The Rockies' offense scored 23 runs in a three-game home set against the Blue Jays, but they predictably struggled on the road and against Kelly, who has a 1.89 ERA and 28 strikeouts in 19 innings over three starts against Colorado this season. Rookie Hunter Goodman’s RBI single in the fifth off Kelly and Elias Díaz’s RBI double in the ninth off Paul Sewald made the final close, but the contest was always steep.

“He’s a great pitcher who historically has pitched very well against us,” Lambert said. “I knew that going into the game. Hats off to him. He outpitched me today.”