CHICAGO -- For most of this season, Keegan Thompson has remained in a multi-inning relief role. Cubs manager David Ross maintained that he wanted to leave this particular bullpen weapon alone, using him as a dominant bridge to the late innings or as insurance for a start gone awry.

The landscape has changed. And Thompson now has some runway to show what he can do as a consistent part of the rotation.

"It's going to be fun," Thompson said with a smile after the Cubs' 7-5 win over the Cardinals on Thursday night.

After that initial reaction to the opportunity at hand, the pitcher reverted back to the season-long script.

"But, like I've said before," Thompson continued, "whether it's starting, relieving or whatever, I'm just trying to go out there and throw strikes and give the team a chance to win."

With veteran lefties Wade Miley (left shoulder) and Drew Smyly (right oblique) both on the shelf at the moment, the Cubs plan on giving Thompson a more extended look as a starter. The righty has been dominant in the bullpen, but his success -- combined with the rotation setbacks -- necessitated this new path.

Against the Cardinals, the 27-year-old Thompson set career highs in both innings (5 1/3) and pitches (89) and walked the last two hitters he faced in the sixth prior to being pulled. He was charged with three runs -- one scored after his departure -- and found ways to overcome some command lapses to hold the line for the Cubs.

"He did a really nice job of giving us a good chance to win," Ross said. "Whether he ran out of juice there at the end or not, it looked like the ball was still coming out really well. He just lost command there at the end. We tried to push him a little bit longer. But, really nice outing."

The starting cast is thin at the moment behind Kyle Hendricks, Marcus Stroman and Justin Steele. Rookie Matt Swarmer is currently one start into his career and Mark Leiter Jr. offers another depth option in the bullpen. Alec Mills (right quadriceps strain) is nearing the end of a Minor League rehab stint with Triple-A Iowa.

With a doubleheader looming against the Cardinals Saturday, a source said the Cubs are "definitely" considering top pitching prospect Caleb Kilian (No. 5 on Chicago's Top 30 prospects list, per MLB Pipeline). Kilian is not on the team's 40-man roster, but will need to be added over the offseason anyway for Rule 5 Draft protection. Whether it is on Saturday or later, Kilian's arrival is coming.

For Thompson, this is an opportunity for him to further strengthen his place in the long-term picture as a core part of the rotation.

"Look, I like outs," Ross said. "I don't care how we get them and where they come from. He's done a good job of doing that. I love that his confidence built up in the offseason. He came in, had a great spring, took over that kind of middle-relief role and giving us some length out of there. He's having a great season so far."

And in the coming weeks?

"I'm looking forward to many more innings of him dominating," Ross said.

Overall, Thompson has logged a 1.99 ERA this season in 12 appearances (four starts). All four of those rotation turns have come since May 11 as rotation issues have mounted. Up to that point, Thompson had a 1.17 ERA in seven relief outings, covering 23 innings in the process.

As a reliever, Thompson has entered games in the second, third, fifth, sixth and seventh innings this year. He has finished two games and served as an opener of sorts. The righty has also started the season with an MLB-leading six wins and is the first Cubs pitcher since Jake Arrieta (2016) to start a campaign with a 6-0 ledger.

Mills, who was at Wrigley Field on Thursday, has served a swing-man role in the past for the Cubs. He marveled at what Thompson has done.

"That's special," Mills said. "He's making it look easy, I promise you. Maybe I made it look hard. But what he's doing is obviously special."

One key for Thompson has been maintaining a reliever-type routine, even before starts. He has cut out his pregame throwing, eliminating catch or long-toss and limiting his build-up to a warm-up similar to what a pitcher would do when the bullpen phone rings during a game.

From there, Thompson has tried to maintain an aggressive mindset on the mound, taking things an inning at a time rather than overthinking about the second or third time through an order.

“We joke, like, guys are saying he's 'opening' for five or six innings," Cubs pitching coach Tommy Hottovy said. "It's, attack the strike zone and come right at guys earlier with his best stuff, and go as long as he can."