DENVER -- Rockies left-hander Drew Pomeranz said delaying his next start from Wednesday to Sunday is merely a precaution, and the day will come when he proves he can pitch when not at his best.

The Rockies moved him to Sunday and called up righty Guillermo Moscoso to start against the Brewers on Wednesday because Pomeranz is dealing with soreness in a chest muscle. The problem affects his velocity.

"When I try to throw max effort, it bothers me," Pomeranz said. "I could go out there and pitch not at my best, back off a little bit, but what's the point? Might as well take a few days. Of course, it helps to keep my innings at whatever innings limit the have for me."

It's true the Rockies are being careful with Pomeranz, 23, who threw 118 1/3 combined innings in the Majors and Minors last year, his first pro season, and is at 111 1/3 combined between the Minors and Majors this year. But when announcing Pomeranz, 23, was scratched for Wednesday, manager Jim Tracy mentioned that Pomeranz will have to find a way to make it through an April-to-October season. At times, that means pitching through some issues.

At times, coaches and club officials have noticed Pomeranz checking the velocity readings on the scoreboard and seeming less confident when his velocity isn't right. They'd like for him to have the same demeanor and aggression no matter how he feels or what's working in a given game.

Pomeranz responded by saying he has done it before. He had a similar issue in college at Ole Miss, yet he pitched well enough that the Indians drafted him fifth overall in 2010.

"I strained my pec pretty bad, but when your team needs you to pitch, you've got to pitch, and find a way to win," he said.

Pomeranz insisted he has his confidence, despite a 1-7 record and 5.04 ERA in 13 starts. The team is 4-9 in his starts.

"I feel like I've pitched better than 1-7, but that's part of it," Pomeranz said. "As long as we're winning the games I've pitched, it doesn't matter."

The Rockies went to a four-man rotation in late June, but they've managed to avoid having Pomeranz pitch on three days' rest. They've scheduled him around off-days and pushed him back on occasion.

Rosario persevering through pain

DENVER -- Late Tuesday night, Rockies catcher Wilin Rosario's troublesome left ankle was encased in an impressive amount of ice and propped on a chair. His teammates were already filing out of the clubhouse, but it would be a while before Rosario could even hobble to the shower.

But during the game, Rosario was light on his feet and heavy with his swing. His RBI double and impressive solo homer to center field -- the 19th of his rookie season -- were key hits in an 8-6 victory over the Brewers.

Rosario, 23, injured the ankle when he tumbled awkwardly while blocking a pitch at San Diego on July 20. The pain has affected his production to a degree. Already struggling fundamentally, Rosario has been less mobile. In 15 games since the injury, he has hit .200 and seen his season batting average drop 10 points to .244.

But Rosario has hit four home runs, driven in eight runs and knocked three doubles since the injury, and in the 15 games he has played in pain he has lifted his season slugging percentage a point, to .533.

"I don't know what fatigue is or any of those things, but I'm playing, and I like to play," said Rosario, who did not start Wednesday afternoon's game against the Brewers. "When the game starts, the pain goes. It comes back after the game, but not when I'm playing."

Rosario can't let the pain hamper him as he tries to finish his development at the big-league level -- a difficult task for a young catcher, even when he is healthy. It's even tougher with a struggling pitching staff.

Rosario leads the Majors with 14 passed balls. The Rockies also went into Thursday leading the Majors with 66 wild pitches -- 13 more than the second-place White Sox -- and were fifth in baseball in walks with 399. So Rosario has had difficulty catching some pitches, but it's clear the pitchers have had trouble hitting a target.

"The pitchers' command fluctuates periodically," Rockies manager Jim Tracy said. "He's recognizing the fact that when he's set up for a pitch and it doesn't go there, he has to be able to shift, respond and get to it, rather than have it go to the screen on too much of a regular basis."

Toward that end, Rosario said, he is setting up with his feet flatter, which allows him to push to the side quicker. Although his ankle injury makes pushing a little more difficult, he might also be safer with his feet flatter, rather than on his toes.

Rosario said he and the pitchers will look much better as they gain experience.

"Sometimes when you're young and you're working with young pitchers, they might not have the confidence," Rosario said. "But it's going to come. I know them and trust them, and they trust me and know me from coming up in the Minors."

Rosario will be there for them, no matter how much it hurts.

Worth noting

• Rockies shortstop Troy Tulowitzki, working his way back from left groin surgery in June, ran on dirt for the first time on Wednesday morning. He ran the bases and worked on double plays. Tulowitzki is scheduled to accompany the team on a road trip to New York and Chicago next week. He'll continue working out, and at some point will be a candidate for a Minor League injury rehab assignment.

• When the Rockies called up righty Guillermo Moscoso from Triple-A Colorado Springs to start Wednesday's game, they designated righty reliever Mike Ekstrom (0-0, 6.23 ERA in 15 games) for assignment.