Jordan Montgomery pitched his way out of Arizona's rotation and into the bullpen in August after a seven-start stretch in which he posted a 7.88 ERA. Montgomery made four relief appearances for the Diamondbacks after the switch, but with Ryne Nelson landing on the 15-day injured list due to right shoulder inflammation, he is returning to the rotation on Tuesday night to oppose the Colorado Rockies in Denver. Montgomery (8-6, 6.25 ERA) will make his 20th start of the season while Colorado will send Ryan Feltner (2-10, 4.89 ERA) to the mound to try to win for the second time in three outings. In the opener of the three-game series on Monday, the Rockies (58-93) scored a run in the bottom of the ninth inning to win 3-2. It was their fourth victory in five games, all against teams with winning records. The injury bug has hit Arizona (83-67) hard lately. In addition to Nelson, the D-backs placed reliever Paul Sewald on the 15-day injured list on Sunday, retroactive to Thursday, because of neck discomfort on the left side. He would be eligible to return Sept. 27, which would give Arizona an extra arm for the final three games of the season. Arizona also added to its relief corps on Monday, bringing back right-hander Scott McGough from Triple-A Reno and optioning third catcher Adrian Del Castillo to the minors. "[That was] a hard conversation, because [Del Castillo] has been so impactful for us, he helped us win baseball games," Diamondbacks manager Torey Lovullo said. "[The staff told him] not to try to do too much offensively, continue to learn about pitch sequencing and what stuff looks like. But mostly from a defensive standpoint, we challenged him to keep growing." With all of the changes to the staff, the Diamondbacks could use a strong performance from Montgomery, who produced one save and a 4.85 ERA in his four recent relief outings. He has fared well in two career starts against the Rockies, going 2-0 with a 3.09 ERA. Tuesday will be the first time he will pitch in Denver. Feltner has not been as successful against the Diamondbacks -- he is 0-3 with 9.00 ERA in three career starts against them -- but he is pitching well in September: 1-0 with a 2.31 ERA in two starts. The victory came at Milwaukee on Sept. 6, and he then he tossed 5 2/3 innings of two-run ball in a no-decision at Detroit on Thursday. His strong start against the Tigers -- he allowed three hits and two walks while striking out six -- came with Jacob Stallings behind the plate. Stallings is hitting .261 with nine home runs after batting .191 with three homers for the Miami Marlins last season. "It's easier when you're getting results," Stallings said. "My execution has been good all year. There have been some days where the pitcher just beats me or I've beat myself, but overall I've been really consistent." --Field Level Media