But the 23-year-old made the transition look rather seamless.
Stewart field five ground balls, including a pair of impressive plays in the sixth inning, in Colorado's 7-4 loss to Philadelphia, and finished 1-for-3 with a double. It was Stewart's first career start at second base.
"Is he going to be as athletic as Jonny [Herrera] or Q [Omar Quintanilla]? Probably not," Rockies manager Clint Hurdle said. "They're just a little more nimble. As far as athleticism, he did some nice things in Spring Training. We'll see how it works out. He made plays that were there for him.
"It's more about finding at-bats while he's here. We're in a position now to take a flier on some things, and we want to see if he can pull this off."
With nine players on the disabled list and others struggling offensively, Hurdle wanted to insert one of the club's most highly touted prospects into the lineup. This was the case again in Wednesday's series finale as Stewart got the start on back-to-back nights at second.
Stewart, the club's top Draft pick in 2003, impressed the Rockies in his 35-game stint last season. He hit .209 and had one homer and nine RBIs, but showed flashes of his immense talent.
In 46 games with Triple-A Colorado Springs this season, Stewart ripped 12 homers with 43 RBIs while posting a .281 average.
When he opened Tuesday's game at second, he became the sixth different Rockies player to start at that position this season. Garrett Atkins, who usually starts at third, played 8 1/3 innings at second on April 29 at San Francisco.
Last season, the Rockies trotted out four players to second -- Kaz Matsui, Jamey Carroll, Clint Barmes and Quintanilla.
"I'm excited about the opportunity," Stewart said. "I'm looking forward to the challenge. I'm going to work as hard as I can at it."
Andy Jasner is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.