CHICAGO -- Cubs manager David Ross didn’t want Keegan Thompson to feel like Saturday was his one and only opportunity to prove himself as a starter.

Thompson pitched well his first two stints in Chicago this season, going 3-2 with a 2.21 ERA in 27 appearances, but that was exclusively as a bullpen arm (besides one start on May 4) for a team that still had hopes of competing for a National League Central title. This time around, Thompson is auditioning for a future spot in the rotation, one that won’t be awarded or taken away in his first start back with the big league club.

“I don't think there's any real pressure on [him], like, ‘This is the one shot you get to be evaluated,’” Ross said before the Cubs’ 4-2 loss to the Royals on Saturday afternoon at Wrigley Field. “I think these are moments to come up and prove yourself, right?”

The long leash Thompson should get from his manager will go a long way toward helping him grow comfortable in his new role, especially considering some of the struggles he went through in his first outing back with Chicago.

Thompson threw 73 pitches over four innings of work. In each of his first three frames, Kansas City got a runner to third (and multiple runners on base in the first two), but Thompson managed to limit the damage to just two runs on five hits, two walks and one wild pitch. He only managed one strikeout on the day, but that three-pitch punchout of Andrew Benintendi displayed the control and power the Cubs hope will come in more than just flashes. And once he got rolling, Thompson retired each of the last six batters he faced.

“I thought he did a nice job of pitching out of the jam in the first,” Ross said. “Second [and] third, only allowing one run with nobody out was really impressive. Getting the soft ground ball to first, the punchout and then that final out, he had to work pretty hard there. I think it took a lot out of him.”

But some growing pains were apparent. Thompson had trouble finishing off batters in the first inning, allowing two hits and a walk after pulling ahead in the count on all three. He didn’t fool many Royals hitters either, as he picked up only four whiffs and seven called strikes.

That first frame was especially challenging for Thompson, when he gave up a single and a double and allowed a run to score on a wild pitch just five pitches into his start. So, a bit of irritation boiled over later in the inning. Frustrated with a call on what he thought was strike three to Ryan O’Hearn, Thompson showed some frustration on the mound that earned him a word from home-plate umpire Jerry Meals.

“I was frustrated from all the foul balls from the guy before him and that batter,” Thompson said. “I thought it was a good pitch. I was frustrated. I yelled -- I don't know if I yelled at him or not -- but that was all it was. I was just frustrated.”

“Keegan may have made a gesture or said something, I don't know,” Ross said. “I just saw [Meals] yell at my pitcher, so I went out there to see what was going on.”

Those are the pains Thompson and Chicago will have to learn to deal with, though, because behind Kyle Hendricks -- and almost certainly Adbert Alzolay -- the future of the rotation is still uncertain. With the Cubs well out of playoff contention, the last month-plus of the season is meant for young arms like Thompson and Justin Steele to show they’re big league starters.

Thompson said being sent down to Iowa on July 27 was a little disappointing because he’d only just gotten his first taste of the Majors. However, the success he had in Triple-A (four starts, 14 2/3 innings, 16 strikeouts, 0.00 ERA) gave him even more confidence that he could succeed as a Cubs starter.

So, sure, Thompson hoped he would’ve looked stronger on Saturday. Fortunately, it won’t be his only chance to prove himself.

“I can get guys out,” said Thompson, referring to what he plans on showing the coaching staff. “I can go through the lineup more than one or two times out of the bullpen. If [you get through] the lineup three times, then you've had a pretty good day.”