When Brewers prospect Johnny Hellweg was sent for Tommy John surgery late last month, it was an unfortunate way to open the door for someone else to step up in Nashville.

"I was basically the sixth guy," said Brad Mills. "I'd step in when needed in a doubleheader, but once that happened, they came to me and said, 'You're the guy now and that's your spot."

Mills has pitched more like an ace than a sixth man since replacing Hellweg, and Tuesday was yet another example. The 29-year-old left-hander struck out eight, walked one and allowed just one hit in a combined two-hit shutout as the Triple-A Sounds blanked the Cubs, 8-0, at Principal Park.

"When [Hellweg] went down, I stepped in and ever since then, I've found my footing, gotten more comfortable in the role and I'm enjoying it," Mills said. "It's been a good fit, I like my pitching coach, we've worked well together, and so it's really been a good year so far."

Mills earned the win on April 26 in his first start following Hellweg's elbow injury six days earlier. He pitched six hitless innings against New Orleans on May 1, limited Colorado Springs to four hits over seven scoreless innings May 8 and turned in another gem on Tuesday, throwing 55 of his 84 pitches for strikes before giving way to Michael Blazek, who struck out two and allowed one hit over the final three innings for his first save.

Mills said he relied more on his secondary pitches Tuesday after his fastball command felt off.

"Obviously the results were good, but this was not my best command effort I've ever had," he said. "I was able to keep it close and put up some zeros."

Originally drafted by Toronto in 2007, Mills made his Major League debut in 2009 and has since appeared in 15 games over parts of four seasons for the Blue Jays and Angels. Toronto traded the lefty to Los Angeles for Jeff Mathis in 2011, and he was claimed off waivers by Texas last March before signing with Milwaukee as a free agent in January.

"It's always good being with a new team kind of trying to prove yourself again," Mills said. "Some of the guys here, they've been playing together for a while, so it's good to get off to a good start. I was kind of in limbo for a while coming out of the 'pen and making spot starts."

Thus, he brings a veteran presence to a role previously occupied by Hellweg, a hard-throwing 24-year-old ranked as Milwaukee's No. 9 prospect after claiming 2013 Pacific Coast League Pitcher of the Year honors.

And while Hellweg could hit 98 mph with his fastball, Mills said he's more concerned with turning in quality starts.

"My focus is always -- as a starter who doesn't throw hard -- if I can throw strikes, I can keep my team in the game," Mills said. "Giving them a chance, making sure the other team is swinging the bat, and hopefully saving the bullpen. The ones that kill you are when you have early outings -- those hurt your bullpen -- so I want to give our team a chance, throw some strikes and see where it takes me."

Mills took that approach Tuesday, picking off Cubs leadoff man Matt Szczur after a walk in the first. He worked a 1-2-3 second before allowing his only hit of the game to Chris Rusin, Iowa's starting pitcher and reigning PCL Pitcher of the Week following his no-hitter on May 7. Rusin reached on a two-out single up the middle, but Mills kept rolling, pitching around a leadoff error in the fourth. He struck out the side swinging in the fifth and whiffed the final two batters he faced in a perfect sixth to end his afternoon. Logan Watkins doubled off Blazek to lead off the ninth and was the only Cubs batter to reach second.

"I just felt like fastball command wasn't on point," Mills said. "Some games you go out and you can put the fastball wherever you want. And that's your focus as a pitcher -- commanding the fastball. But luckily I was throwing my secondary pitches -- my changeup and curves. I was able to throw those for strikes whenever I wanted. Ideally, I'd like to have better fastball command."

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Despite the command struggles, Mills managed to follow Jimmy Nelson's gem for Nashville a night earlier, when the righty held Iowa to a pair of hits and struck out nine over six innings. Nelson also spoke about overcoming early command issues.

"It comes and goes," Mills said. "There's games you're going to go out there and feel like you don't need to think about your aim. And sometimes you're fighting yourself, you're out of rhythm and working harder, and that's how it was today."

Nashville broke the game open in the fourth when Taylor Green doubled home Sean Halton, Kevin Mattison plated Hector Gomez with a sacrifice fly and Pete Orr added a two-run single. Mills himself laid down a sacrifice bunt in the sixth that helped Matt Pagnozzi score when Rusin threw the ball away. Gomez tacked on a two-run homer in the seventh, his fourth, for more insurance.

Blazek turned in his third straight scoreless appearance following a rough outing on May 1, impressing Mills.

"He's a great arm -- I'm glad hes coming in behind me," Mills said. "With runners on, he's a guy I want coming in. I'm happy to see him get some extended work and do well."