Roberts, who turned 27 on March 9, has made six appearances for the Isotopes, allowing 17 hits and six runs (four earned) to post a 3.27 ERA. He was scored upon in two of his six appearances. He was selected by the Rockies in the 25th round of the 2010 First-Year Player Draft out of Middle Tennessee State University.
Roberts has a Minor League record of 21-8 with a 2.37 ERA (304.0 IP, 80 ER) in 199 games, including two starts. He will wear number 67.
Rondon was recalled from Triple-A Albuquerque April 27 and pitched in two games. He had one Major League appearance prior to this season, a one-inning stint for the St. Louis Cardinals at Los Angeles (NL) on June 29, 2014. The Rockies claimed the 27-year-old Venezuela native off waivers on Nov. 3, 2014.
The Rockies have a full 40-man roster.