PEORIA, Ariz. -- Two of the most meaningful outings thrown by Padres pitchers this spring took place on a Peoria Sports Complex back field Tuesday morning, 20 minutes apart.

In that 20-minute span, all the optimism surrounding an encouraging showing from Dinelson Lamet faded when left-handed reliever José Castillo exited his simulated game after six pitches because of forearm tightness. Castillo, who has pitched only one game over the past two seasons because of an assortment of injuries, will be re-evaluated on Wednesday, the team said.

It was Lamet who took the mound first, facing hitters for the first time since he exited his last start of the season against the Giants last September. The Padres have been building Lamet slowly this spring. He had a platelet-rich plasma injection in October and said doctors told him his late-season shutdown last year would help him avoid Tommy John surgery.

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Lamet was clearly thrilled to be back on the mound Tuesday, even if he was shaking off some rust. He threw 15 pitches, including three or four changeups, but no sliders. (He's been throwing sliders regularly in his bullpen sessions, but the team asked him to hold off on Tuesday.)

Lamet, whose fastball sat at 96 mph, allowed singles to teammates Jorge Mateo and Tucupita Marcano and induced a couple whiffs. When he finished his day with a high heater to Marcano, he leapt off the mound in a rare show of emotion from the unflappable right-hander.

"Facing hitters actually made me feel more comfortable, after not having faced them for five months and not really having as much activity," Lamet said through a team interpreter. "Being able to face them and see a hitter in the box helped, actually."

Without question, Tuesday was a positive step for Lamet. But his current progression begs the question: Will he be built up in time to crack the Opening Day roster? As things stand, Lamet is a couple steps behind the rest of the Padres rotation.

If he's not ready by Opening Day, that's just fine with the Padres and Lamet.

"It's going to be an ongoing discussion with our medical team, and I think that's a good thing," Lamet said. "We have really good communication on the subject, and we're taking everything day by day. I know I'm going to be ready to help in the season. But at the same time I want to make sure that I'm progressing well. That's really the stance that we've been taking.

"Once I join the team and once I'm ready to go and once I'm pitching, I don't want to go backwards."

Speaking on MLB Network Radio on Monday, Padres general manager A.J. Preller expressed the same sentiment.

"We're going to be smart in general," Preller said. "We have a lot of depth. April 1 is not the important date. We keep talking about wanting to play into October and making sure Lamet is able to pitch for us. So far, he's been right on track."

As for Castillo, Tuesday's setback is a particularly gut-wrenching one -- considering his upside and considering the work he has gone through to recover from a trio of ailments over the past two years. Castillo has been limited to two-thirds of an inning in that span because of a left flexor strain, a left lat strain and a left middle-finger injury.

The Padres have been enamored with Castillo's big-time stuff since his 2018 debut season, when he struck out 52 hitters over 38 1/3 innings with a 3.29 ERA. At the time, team officials wondered whether his electric fastball/slider combo might make him closer material.

Injuries have prevented Castillo from a chance to realize that potential, and the latest setback came Tuesday morning. Castillo threw his sixth pitch, and then pitching coach Larry Rothschild ended the session early, as a dejected Castillo went into a crouch behind the mound. He left the field shortly thereafter, accompanied by a team trainer.