He was promoted to the National League prior to the 1999 season along with Paul Nauert to fill vacancies left by the retirements of Jim Quick and Harry Wendelstedt.

Nelson served as the second base umpire when Chicago Cubs pitcher Carlos Zambrano threw a no-hitter against the Houston Astros at Miller Park on September 14, 2008.

[2] Nelson was the plate umpire for a Detroit Tigers–Kansas City Royals game on September 27, 2012, when Tigers pitcher Doug Fister set an American League record by striking out nine consecutive batters.

[4] Nelson was chosen as one of the umpires for the one-game Wild Card playoff between the Atlanta Braves and the St. Louis Cardinals on October 5, 2012.

[6] Nelson was the home plate umpire for the 2015 National League Wild Card Game between the Chicago Cubs and Pittsburgh Pirates.