HOUSTON -- Tyler Colvin's strong spring gave reason to believe he could have a breakout year with the Rockies, after he struggled with the Cubs last season.

Colvin, 26, hit .373 and posted a .612 slugging percentage in Spring Training. ACTA Sports recently released figures saying that players who slug 200 points above their career marks have a 60 percent chance of a breakout year. Only a couple of hitless games at the end of the Cactus League schedule pulled Colvin below the threshold (his career slugging percentage was .466 going into the year).

Colvin hit .150 last year but revamped his swing, as he showed while lashing a hard single to left as a pinch-hitter on Saturday night. Colvin made his first Rockies start Sunday, in center field and in the leadoff position, against the Astros.

Manager Jim Tracy likes the idea of Colvin at the top of the order.

"He's got enough speed to steal a base," Tracy said. "It's an intriguing aspect of having a guy up there that has the type of power that he has. When they come back around to the top of the lineup when we have men on base, they're going to have to respect his power."

The Rockies are sticking with center fielder Dexter Fowler as he works through some poor hitting habits that crept in during Spring Training, but the club is well-served by finding ways to put Colvin on the field. Colvin, a left-handed hitter, can play all three outfield positions, as well as first base.

Colvin said hitting the other way, as he did in an encouraging rookie season in 2010 with the Cubs (.254, five triples, 20 homers) and after he reworked his swing this spring, fits with the assignment of batting leadoff. Going into Sunday he had a .248 batting average and .307 on-base percentage as a leadoff man in 25 Major League games.

"It's just a matter of believing that all the work I put in is going to pay off, and I need to stay focused where I need to stay focused, not stray away," Colvin said.

Helton sits out series finale against Astros

HOUSTON -- Rockies first baseman Todd Helton was out of the starting lineup Sunday after playing twice against the Astros, but he knew he had work to do.

Helton, who doubled in Friday night's season opener and went 0-for-4 with an RBI Saturday night, was not happy with his at-bats as each game progressed.

"I'm disappointed in my swings at the end of the games, both nights," Helton said.

Jason Giambi started at first on Sunday, as manager Jim Tracy rested not only Helton, but veteran second baseman Marco Scutaro and catcher Ramon Hernandez. Jonathan Herrera and rookie Wilin Rosario -- who threw out Jordan Schafer on a strikeout-double play in the first inning before connected on a two-run homer in the fourth -- made their first starts of the season.

Additionally, Jordan Pacheco started at third instead of Chris Nelson.

Rockies to limit innings for Pomeranz

HOUSTON -- Rockies left-hander pitcher Drew Pomeranz is scheduled to pitch for Double-A Tulsa at Corpus Christi on Tuesday night.

Pomeranz, 23, a rookie, is the club's fifth starter. The Rockies didn't need him the first time through the rotation, and they are trying to limit and pace his Major League innings.

Last year, Pomeranz threw a total of 119 1/3 innings between the Minors and the Majors -- where he threw 18 1/3 innings and went 2-1 with a 5.40 ERA in four starts for Colorado. It was his first professional season.

The Rockies will give Pomeranz his 2012 Major League debut next Sunday at Coors Field against the D-backs. To make sure he is a part of the rotation throughout the season, the Rockies will skip Pomeranz on some occasions.

Worth noting

• Josh Outman, who suffered a sprained right oblique while vomiting during a bout of food poisoning, played catch from 90 feet on Saturday and is taking Sunday off.

Outman, a versatile left-hander who went 3-5 with a 3.70 ERA in 13 games (nine starts) for the Athletics last year, is making progress, according to Rockies head athletic trainer Keith Dugger. However, he yet to be scheduled for game action at extended Spring Training in Scottsdale, Ariz.

• Rockies outfield prospect Charlie Blackmon, who was challenging for a roster spot before suffering a right big toe injury during Spring Training, will play in extended Spring Training games this week. The Rockies have changed his shoes and added orthotics. Blackmon hit .255 in 27 games last year before suffering a broken right foot.

• Left-hander Jorge De La Rosa, scheduled to return in late May or June from elbow surgery, is scheduled to throw a 55-pitch bullpen session on Monday -- 20 pitches, then rest, then 15, then 20. He should participate in a simulated game April 16 or 17.