Nelson was not in the lineup for Wednesday night's exhibition game against Team USA's World Baseball Classic team. Arenado, 21, who played at Double-A Tulsa last season, carried a .412 average, four homers and eight RBIs into his start Wednesday night.
But last year, Nelson made a late Spring Training push to earn his first career Opening Day start. Although he battled a wrist injury early and missed time in July and August with an irregular heartbeat, Nelson managed a .301 batting average, .352 on-base percentage, nine homers and 53 RBIs in 111 games.
"That's competition -- it makes everybody better," Nelson said. "I don't know one person who wouldn't want to compete harder to try to keep his job when somebody's trying to take it. I like to compete."
Nelson said he expects to start spring slowly. After his first games in the Majors in 2010, then-Rockies manager Jim Tracy felt Nelson was not getting full power from his lower body in his swing. Nelson has developed a leg kick, which has given him enough bat speed that many believe he can produce 20 homers in a season. But the kick requires timing.
"With that leg kick, it takes time," Nelson said. "It's not going to happen tomorrow. It's not going to happen overnight. I've just got to see more pitching."
Last year, Jordan Pacheco was the guy getting notice early in spring. Pacheco ended up playing third when Nelson was hurt and batted .309. Both ended up with enough at-bats to have an impact. Understanding that the guy he is competing with is a teammate and not an enemy, Nelson said he doesn't begrudge Arenado his success.
"I love the guy," Nelson said. "He's good and a good teammate."
The situation bears watching, because Nelson is out of Minor League options, meaning he can't be sent down without being exposed to other teams through waivers. The Rockies are known to be seeking pitching, and they could seek to trade Nelson if Arenado forces his way into the starting job.
Thomas Harding is a reporter for MLB.com. Read his blog, Hardball in the Rockies, and follow him on Twitter @harding_at_mlb. This story was not subject to the approval of Major League Baseball or its clubs.