D-backs' Clay Buchholz scratched with right arm tightness

DENVER -- Arizona Diamondbacks right-hander Clay Buchholz was scratched from Thursday's start because of tightness in his right arm.

Matt Koch started in his place.

Buchholz, who signed a minor league deal with Arizona on May 4, is 7-2 with a 2.01 ERA. He is 5-1 with a 1.66 ERA in nine starts since returning from the disabled list on July 24.

Koch made his 12th start of the season Thursday against the Colorado Rockies, but he left after allowing four runs and eight hits in three innings.