DENVER (AP) Colorado Rockies top pitching prospect Jon Gray is expected to make his major league debut Tuesday night against the Seattle Mariners.

Gray, 23, was the third overall pick in the 2013 draft. The hard-throwing right-hander was 6-6 with a 4.33 ERA in 21 games - 20 starts - for Triple-A Albuquerque this season. In his last six starts he is 3-1 with a 2.70 ERA and 38 strikeouts.

Gray has moved quickly through the Rockies' system. He was 4-0 with a 1.93 ERA in nine minor league starts in 2013 and was 10-5 with a 3.91 ERA in 24 starts with Double-A Tulsa in 2014.

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He was Colorado's highest pick since right-hander Greg Reynolds was taken second overall in 2006. Reynolds won only six games in his major league career.