CHICAGO -- It was not so much that Cubs manager David Ross wanted to embrace the role of spoiler this weekend. Having younger players taste September baseball with October implications mattered more.

In the opener of a twin bill against the red-hot Cardinals, Ross gave some extra leash to rookie Justin Steele. There were growing pains in an 8-5 loss on Friday afternoon at Wrigley Field, but it was another outing for Steele to study.

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"They're the hottest team in baseball right now," Ross said. "They're coming in playing really good baseball. I think it's a great environment for a lot of these guys, the young guys."

Steele surrendered a trio of home runs -- one each to Paul Goldschmidt, Tyler O'Neill and José Rondón -- and St. Louis extended its winning streak to 13 games. The Cardinals are chasing a spot on the October stage, while Chicago has been operating with '22 in mind.

Looking ahead to next season, the 26-year-old Steele will give the Cubs an internal rotation piece to consider, along with righties Adbert Alzolay and Keegan Thompson. The only two arms with starting jobs lined up next year are Kyle Hendricks and Alec Mills.

Adding to that group will be at the top of the Cubs' offseason to-do list.

"What the rotation looks like," Cubs president of baseball operations Jed Hoyer said prior to Friday's doubleheader, "free agency and the trade market will help determine that."

As for Steele, Alzolay and Thompson?

"Have they proven enough to know they’ll be a big part of next year’s team? Yes," Hoyer said. "In exactly what role? I think that’s what we have to determine."

Earlier this week, Ross said he could foresee a situation where "maybe one or two" of that trio cracks the Opening Day rotation. All three have also shown they can be valuable as multi-inning bridge arms in the bullpen.

Steele, in particular, was impressive when he broke into the big leagues as a reliever across April and May. It filled a need at the time for Chicago, but it also helped ease the lefty into the bigs while monitoring his innings.

As a reliever, Steele posted a 2.03 ERA with 21 strikeouts and seven walks in 13 1/3 innings (11 appearances). Following a buildup process at Triple-A Iowa, he returned for a rotation audition last month, and he has experienced inconsistent results.

"It's definitely different being a starter and a reliever, right?" Ross said. "They can get hitters out. Now it's, 'How can I do that getting exposed every fifth day for multiple innings?' I think that's a difficult task and why those guys get paid a ton of money."

On Friday, Steele struck out five and generated 10 swinging strikes in five innings, but he was charged with six runs, all on the three homers. That gave him a 5.89 ERA in 36 2/3 innings (eight starts) since moving into the rotation.

“I thought he threw the ball really nice,” Ross said. “It just looked like he ran out of steam there at the back end, trying to let him work through and push through. He wasn't able to execute and do it, but the first four innings I thought were pretty darned good.”

Steele said he immediately went to work on dissecting his performance after exiting his start. The lefty noted that physically, he felt great -- a positive sign near the end of his first full big league season.

Beyond that, Steele noted that he made mistakes -- issuing a walk to pitcher J.A. Happ in the leadup to Goldschmidt’s third-inning homer was one -- but he added that this would be a start where he could easily distinguish the good from the bad.

And Steele agreed that part of the good included having a chance to face a team playing as well as St. Louis at the end of a year of development.

“Absolutely,” Steele said. “The first thing I was doing is looking back at all the good I can take from it. That's a good lineup. ... They've been on a hot streak here lately. They're swinging the bat well. I mean, yeah, there was a lot of good to take from that outing, for me.”