But to call Sullivan a "fourth outfielder" is misleading. If anything, it's a shared role with Ryan Spilborghs. But with the way all five Rockies outfielders function and blend, and the way the team as a whole is built for versatility and consistency on offense, Sullivan's function defies the notion of any kind of "reserve" role.
Sullivan has embraced his part in the outfield cog as wholeheartedly as he once embraced the starting center-field job he won during the 2005 season.
"When you have an established role, it's a benefit rather than not being established," Sullivan said after Friday's victory over the Royals. "Last year, I think Ryan Spilborghs and myself both took the roles we had very seriously and we kind of challenged each other and pushed each other in-season. We both had some good success."
Spilborghs and Sullivan can actually bring back memories of some of the classic outfield platoons -- perhaps even the John Lowenstein-Gary Roenicke tandem that thrived under Earl Weaver for the late '70s and early '80s Orioles. They're not sharing a starting job, and they're not playing any kind of straight platoon, but they are mixing and matching, complementing Matt Holliday, Willy Taveras and Brad Hawpe, and enabling the Rockies to keep in stride both defensively and at the plate, regardless of the permutations.
"Part of it is all of us realizing our strengths and our weaknesses," Sullivan explained. "And being able to rely on the guy next to you to pick you up. Having Matty, he's the staple of the outfield. Willy, he's our speed guy. He's great defensively. He's got a great arm. And obviously, Brad brings the total package as well. We just have to use those tools that we each have and that we're gifted with, and obviously, we'll be successful."
The success took the Rockies all the way to the end of October last season, with Spilborghs and Sullivan in center during the playoff push while Taveras dealt with a quad injury. And although he was back in action for the National League Championship Series, when the World Series finally came to Colorado, it was Sullivan starting in center for the Rockies in Game 3.
Having spent his time in the leadoff role, it's not hard for Sullivan to jump into Taveras' shoes there. He may not keep up with Taveras' speed stealing bases, but Sullivan is always a double-digit threat, employing some of the same baserunning acumen and some of the same strengths as a hitter.
"I just try watching [Taveras], and he has such good success with it. I just try and mimic him and use him as my measuring stick," Sullivan said. "He's got such good speed and he uses it so well. I think you can learn a lot from watching him play."
And as a part of Colorado's five-man outfield core, Sullivan never missed a step in the Rockies' record-breaking defensive season, giving the Rockies constant strength with the glove.
"Defensively, our outfield's one of the best in baseball, if not the best in baseball," Sullivan said. "Arm-wise as well. I think we all compliment each other and challenge each other. When you hold each other accountable, and you're friends more than teammates, I think that's a big help."
That accountability was central to the Rockies' success last year, and it both grew out of and helped fortify the close sense of team the Rockies embodied. With more and more players settling in Denver, concepts of both "team" and "home" are everyday realities, not just baseball goals.
"I lived in Denver, worked out with Holliday, [Garrett] Atkins, Spilborghs, [Jeff] Francis; we all worked out at Coors Field," Sullivan said of his short, but full offseason. "Just being around the guys, with this group of guys, it's friends, it's not just teammates. I think that helps with accountability. It's a lot easier to hold your friends accountable."
Sullivan's year-round focus and approach to consistently expanding and improving his game helped make his a valuable part of the roster in '07, and the dependability along with the ambitious pursuit to attain high goals is not lost on his manager.
"I like the way Cory's going about his game," manager Clint Hurdle said Friday. "I like the fact he wants to play more. The fit for him on our team is what it is right now. It's something he's adapted to. He provides solid defense at all three spots out there. He can do some things offensively, he's honed down his swing, he's taking better pitches, more under control. He's becoming a better player because he's becoming smarter. He's making some adjustments."
The great players are always trying to be better, and Sullivan doesn't hesitate to study for an edge, an element to incorporate into the team's game. He's trying to take more time in right field during Spring Training, not necessarily out of the expectation that his role would shift in that direction, but in preparation for any unexpected situation.
"Right now, on an everyday basis, you can always get better in baserunning," Sullivan pointed out. "Defensively, you can make yourself more rounded -- left, center and right field for myself now -- and at the plate, just working on comfort. Right now, I'm not real comfortable at the plate, but I think that the whole point of Spring Training is to find that comfort level and build toward it during the season. You don't have to come in to Spring Training and be full tilt, because then you might stall come the beginning of the season. Right now, I'm just trying to work on that comfort level, see pitches and build a solid base for March 31 this year."
Owen Perkins is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.