Arizona (40-32) won the series opener 7-4 on Monday night to extend its lead in the National League West to two games over the Los Angeles Dodgers.
Paul Goldschmidt drove in two runs and is batting .426 (29-for-68) with eight homers and 18 RBIs in his last 17 games.
The Angels (38-35) gave up the first six runs of the interleague series opener before dropping their seventh game in the past eight to fall 8 1/2 games back of the Seattle Mariners for the second wild card in the AL. They were 3 1/2 games back on June 9.
"It's tough to spot them six," Angels manager Mike Scioscia told reporters after the loss Monday.
Koch (5-3, 4.09) wasn't expected to be part of the rotation this spring, but an arm injury to fellow right-hander Taijuan Walker prompted the club to recall Koch from Triple-A Reno on April 20.
He was 2-0 with a 2.13 ERA after four starts, lost three straight in mid-May, but has regrouped with the help of exceptional run support. The Diamondbacks have combined for 36 runs in his past four starts.
"You always have to be ready for your opportunity," Koch told the told Sioux City Journal last week. "You never know when it's going to come, how early or how late it is, you just have to be ready for it, whenever it is, and try to take advantage of it."
Koch's spot in the rotation isn't set in cement, as veterans Shelby Miller (Tommy John surgery) and Robbie Ray (right oblique strain) are making rehab starts and nearing their returns.
Despite his recent success, his first career appearance against the Angels could determine whether Koch remains in the rotation. He said he's not focused on that aspect of his performance.
"All I try to do is just get ready for that game and do all I can to keep the team in the game, and try to win," Koch said. "I can't really worry about all the other stuff that's going on or your focus isn't going to be on what you need to do."
Koch would be more than willing to occupy a spot in the bullpen if it meant staying with the Diamondbacks.
"I want to be part of the team and if it's best for the team for me to go to the bullpen I'll do it, and if it's best for me to stay in the rotation I'll do it," he said. It's whatever they think will help the team most."
The Angels are scheduled to send 28-year-old right-hander Felix Pena to the mound for his first major league start.
For the third time this season, Pena (0-0, 10.13) was recalled from Triple-A Salt Lake on Friday. He has made two relief appearances with the Angels this season totaling 2 2/3 innings. Nine of his 10 appearances for Triple-A Salt Lake this season have been as a starter, and he's 1-2 with a 3.51 ERA for the Bees.
Pena was acquired from the Chicago Cubs in October after making 36 relief appearances over the past two seasons. He has never faced the Diamondbacks.