"I could definitely tell there is some stuff," Cahill said when asked if there was a difference with his new delivery. "Just where I have to set my sights on pitches has to change a little bit, because the ball doesn't run as much."
Rockies starter Jhoulys Chacin, who was limited to just 11 starts last year due to a shoulder injury, retired the D-backs in order in the first inning before running into trouble in the second.
Mark Trumbo led off the second with a double, and one out later Cody Ross drove him home with a single to center. After Chacin was removed in favor of Jason Gurka, Ross wound up coming around to score on a single by Gerald Laird to give the D-backs a 2-0 lead.
Vidal Nuno, who is also competing for a spot in the D-backs rotation, did not fare as well as Cahill. The lefty allowed a pair of runs on five hits in two innings.
Arizona's No. 1 prospect Archie Bradley looked strong, striking out three and allowing just one hit in two scoreless innings.
"It's always good to get it started that way and I feel really good and comfortable out there," Bradley said. "So hopefully I can just keep that going."
Eddie Butler, one of the Rockies' top prospects, came on in relief and allowed a go-ahead two-run home run to Danny Dorn in the fourth. Butler completed two innings, allowing four hits.
D-backs Cuban free-agent sign Yasmany Tomas was 0-for-3 at the plate. In the field, he made four nice plays at third and mishandled one to his backhand side.
D-backs up next: The battle for spots in the rotation continues Friday when the D-backs play host to the A's. Left-hander Robbie Ray, who was acquired from the Tigers during the offseason, will start while two other rotation candidates -- Randall Delgado and Allen Webster -- are also slated to pitch in the game.
Steve Gilbert is a reporter for MLB.com. Read his blog, Inside the D-backs, and follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.