DENVER -- Chad Bettis has been pitching ahead of Jon Gray in the Colorado Rockies' rotation and could have started against the Arizona Diamondbacks.

But the Rockies made a change. They will have Gray start the rubber game of the series and send Bettis to the mound Monday against the San Francisco Giants.

"Bettis has pitched a lot against Arizona this year. Gray hasn't, so that was the biggest reason," Rockies manager Walt Weiss said Saturday in his pregame media session.

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Understandably, Weiss left unsaid what Bettis' results have been against the Diamondbacks. In four starts against them this season, Bettis 1-0 with a 7.54 ERA (19 earned runs, 22 2/3 innings). He has allowed 37 hits in those outings.

Enter Gray, whose only career start against the Diamondbacks was in September 2015.

In his first full season in the majors, Gray is 9-6 with a 4.41 ERA in 138 2/3 innings with 150 strikeouts, a franchise record for a rookie pitcher. Gray worked six scoreless innings against the Los Angeles Dodgers while winning his last start Monday and is 1-0 with a 1.50 ERA in his past two outings with six walks and 18 strikeouts in 12 innings.

"My arm's feeling pretty fresh," Gray said. "I feel like it's the beginning. I think I'm doing a better job of resting, not throwing so much during the week. I think it's saving a lot of bullets."

Gray's slider can be a wipe-out pitch and the one he relies upon to get strikeouts. But against the Dodgers, he got strikeouts with his curveball and changeup and said his four pitches in that game were as good as they have ever been together.

"It's kind of a good thing that I didn't get a chance to really go to my slider whenever I needed it," Gray said. "I was able to work with other pitches and get outs and I think that's going to help me in the long run. I think that helped me the last outing, I used all my pitches to get strikeouts. The more unpredictable I can be with not going to my slider every time I get two strikes, (the better)."

Archie Bradley will oppose Gray and start for the Diamondbacks. Bradley is 5-8 with a 4.95 ERA. In his last outing last Sunday against Cincinnati, Bradley picked up the win as he allowed two runs and five hits in six innings with no walks and three strikeouts in Arizona's 11-2 victory.

In three career starts against the Rockies, Bradley is 1-0 with a 4.38 ERA. His two career starts at Coors Field have come this year, and Bradley is 1-0 with a 4.09 ERA in those outings. He gave up four runs in six innings there May 9 and was the winning pitcher in Arizona's 10-5 win and wasn't involved in the decision June 24 when he allowed one run in five innings and the Diamondbacks won 10-9.

The Diamondbacks have been buoyed by the return of center fielder A.J. Pollock, who broke his right elbow shortly before start of the regular season and was reinstated from the 60-day disabled list on Aug. 26. After going 0-for-8 in his first two games, Pollock is 9-for-20 (.450) in his past five games with one homer, three RBIs, seven runs scored and four walks.

"I wanted to come back and be with the guys and contribute to the team in games," Pollock said after going 2-for-5 and scoring twice Saturday in the Diamondbacks' 9-4 victory. "I feel like I've been able to impact the game in little ways."

Pollock was an All-Star for the first time and won his first Gold Glove last year when he set career highs in average (.315), doubles (39), home runs (20), RBI (76), runs (111), hits (192), OPS (.865) and stolen bases (39).

He played 12 rehab games at three levels and got 40 at-bats before making his 2016 debut with the Diamondbacks. After those two hitless games, Pollock has quickly settled back in and is again producing from his No. 2 spot in the lineup.

"I think there's adjustment being in the big leagues," he said. "The stadiums are pretty loud. For your eyes -- you've got to get adjusted to that. Obviously, you've got to make sure you calm yourself down a little bit. I think that was the biggest thing. And slowing the game down, that takes a little bit of time."