CHICAGO -- José Quintana was out in left field on Monday afternoon, working through a long-toss routine in preparation for a bullpen session. His left thumb injury on the eve of Summer Camp seemed perilous for a Cubs rotation fraught with questions.

On Monday night, right-hander Alec Mills -- the starter who assumed Quintana's vacated rotation slot -- baffled the Royals for seven innings to guide Chicago to a 2-0 victory. The win improved the Cubs' ledger to 8-2 on the young season, and the rotation has been a large part of that early success.

• Box score

"I think getting the opportunity is all I needed," Mills said. "Obviously, what happened to [Quintana] is not fun, but that's why I'm here. I'm here to step in and fill in when I need to be, and do whatever I need to do."

• Báez makes jaw-dropping tag: 'I practice this'

Mills limited Kansas City to three hits and did not relinquish a hit to the final 18 batters he faced. The righty struck out four and walked three in the outing, which helped lower the Cubs rotation's ERA to 1.95 and the opponents' average to .156 in 60 combined innings through 10 games.

A solo homer by Kris Bryant in the eighth helped pad the Cubs' lead, and Rowan Wick recorded a four-out save to seal the win for Mills.

Mills has fit within a rotation that is headed by veterans Kyle Hendricks, Jon Lester and Yu Darvish. In Quintana's absence, righty Tyler Chatwood moved up and has been one of baseball's most surprising starters out of the gates. Mills is keeping pace, too.

"You're really seeing a guy that can execute a game plan," Cubs manager David Ross said. "You see a guy that can change speeds. He's not afraid to throw any pitch in any count. He's got huge poise out there for such a young pitcher -- we've known that about him for a while."

Cubs infielder David Bote -- who made a handful of critical defensive gems at third base in the win -- said recently that facing Mills in Summer Camp intrasquad games was not a fun assignment. Bote mentioned the right-hander's "speed discrepancies" as a possible reason for being so confounding.

Along those lines, Mills operates in three very different velocity tiers. His fastballs (sinker and four-seamer) each check in around 89-91 mph on average. When he leans on his slider or changeup, they land in the 78-80 mph range. And then there is his slow curveball, which usually drops in anywhere between 64-67 mph.

Mills developed that curveball last season, when he spun a 1.15 ERA in September and a 2.75 ERA in nine appearances overall for Chicago. The righty continued to hone the slow breaker over the offseason and in Spring Training, and then used the three-month shutdown period to keep refining the pitch.

"Last year at the end of the year," Mills said, "I kind of really started getting more of a feel for that curveball. I think it's been a big thing for me. It's kind of just a different pitch that I thought made me a lot better."

Mills featured the curve 11 times out of his 98 pitches against Kansas City, reaching as low as 64 mph with the offering. That is nearly 30 mph slower than the max velo he reached with his fastball (92.2 mph).

"He attacked the zone early in the count," Cubs catcher Willson Contreras said. "We took their aggressiveness to our advantage. They were swinging and swinging, so we expanded the zone a little bit, and it worked out. Mills has been great to us. I like him a lot."

In his first outing of the season, Mills induced 10 groundouts in six impressive innings against the Reds. This time around, the righty generated nine outs via grounder against the Royals, who originally took Mills in the 22nd round of the 2012 MLB Draft.

Mills made his Major League debut with Kansas City in 2016, but he was traded to the Cubs the following offseason for outfielder Donnie Dewees (traded back to Chicago in March 2019). The fact that Mills blanked the team that dealt him away made Monday's win a little sweeter.

"That was a team that got rid of me a couple years ago," Mills said. "I understand the business. My job is to make it hurt whenever I face them again. It took four years for it to happen, but I'm glad it did."

If Mills keeps pitching like he has out of the chute, helping the rotation continue to be a strength -- rather than a perceived weakness -- then the Cubs may have a tough decision on their hands when Quintana potentially returns.

That internal discussion is still a ways away, though. Quintana has been off the mound three times since his thumb surgery and is scheduled to throw two simulated innings at the South Bend training site on Thursday. There are still plenty of hurdles left in his comeback.

"I hope everybody keeps pitching well," Ross said. "I hope everybody pitches well and makes things difficult, for sure."