KANSAS CITY -- There suddenly is greater responsibility on the shoulders of Royals left-hander Mike Montgomery.

The Royals’ rotation, thin even before Spring Training started, has gotten thinner during Summer Camp. Right-hander Brad Keller, last year’s Opening Day starter, just returned from the injured list [COVID-19] last Friday.

And right-hander Jakob Junis, projected to be the No. 3 starter, went on the IL on Monday. Junis missed the first part of Summer Camp after testing positive for COVID-19, and he will require extra time to get ready for his regular-season debut.

That leaves left-hander Danny Duffy and Montgomery as the only two expected starters in 2020 who are ready to go. Montgomery’s final Summer Camp test came on Monday night at Kauffman Stadium in a 6-3 exhibition loss against the Astros.

• Box score

“Me and Danny talked about it,” Montgomery said. “We definitely have to do our part. We have to eat some innings. Losing those two guys [Keller and Junis] is big. Everyone, including myself, will have to pick up the slack.”

Montgomery had his positive moments, at one point retiring eight of nine hitters. He went 3 2/3 innings overall, giving up four hits and five runs, though only one earned run.

“I definitely had a little more nerves when you face a team in a different uniform,” Montgomery said. “First couple of innings, I was just trying to slow it down and get my delivery down.

“I thought I made some good pitches, but I just couldn’t get that last out. All in all, I think it was OK.”

Montgomery would have had a 1-2-3 fourth inning had it not been for a fielding error when third baseman Maikel Franco threw a bit high to first on a grounder from Yuli Gurriel, and first baseman Ryan McBroom couldn’t bring it down.

Montgomery then allowed two-run home runs to Josh Reddick and former Royals catcher Martín Maldonado.

“[Montgomery] was just getting a feel for the mound early on,” manager Mike Matheny said. “I thought he did a nice job after the start. Unfortunately in the fourth, we had a play we usually make that didn’t get made, and it turns into four runs.

“But he also has to be able to help out his defense there because they are going to make plays. But his strikeout pitch, his changeup, looked really good.”

Reddick hit a sinker that was middle-in. Maldonado jumped a middle-in cutter.

“Definitely mistakes,” Montgomery said. “I fell behind both of those guys. Ramifications of this game are different than regular season. I was just trying to throw as many fastballs as I could. That’s something I might not do in the regular season.”