He allowed three runs on four hits. He struck out one and pitched around three walks to earn his first victory after flourishing in the minors.
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"That was good to see," Roenicke said. "He came out of the first inning still a little different. But as innings went on stuff got better, location got better, I thought he pitched more with his changeup and his breaking ball. Hopefully this is the guy we're going to see."
Hellweg was the Pacific Coast League's pitcher of the year after going 12-5 with a 3.15 ERA in 23 starts at Triple-A Nashville.
The 24 year-old made his major league debut on June 28 in Pittsburgh. The 6-foot-9 right-hander was knocked out after giving up seven runs -- five earned -- and six hits while walking two in 1 2/3 innings of a 10-3 loss. He was also roughed up in a relief appearance and another two starts before being sent back to the minors.
"It feels awesome," Hellweg said. "It feels good to contribute to the team up here. I am going to embrace it a little bit. I am not going to put it behind me yet, it feels good to go out there and put up six innings and give a chance for our team to win."
The Cubs got solo shots from Luis Valbuena and Brian Bogusevic who fell to 16 games under .500 at Wrigley Field. With the loss, the Cubs dropped behind the Brewers for last place in the NL Central.
Cubs starter Jake Arrieta (2-2) pitched five innings and allowed four runs on three hits. He also gave up three walks and hit one batter. The 27 year-old right-hander was done in by a four-run fourth inning.
Arrieta, who is trying to compete for a spot on the 2014 roster, gave up all three hits in the fourth.
Trailing 2-0 in the fourth, Scooter Gennett drove in a run on a single and Schafer cleared the bases with a triple to right-center to put Milwaukee ahead 4-2.
"First and foremost, I got a little too fine with those couple of walks and I got myself into a situation when Schafer came up," said Arrieta. "(I) just left a sinker right in the middle of the plate and he didn't try and do too much there, he just shot the ball in the gap in the right spot to clear the bases.
Schafer came into the game 3-for-23 against the Cubs this season.
"Well, Schafer is off and on. He comes through with some big hits, I don't want to say much he's been struggling for us, but he has been getting some big hits for us," said Roenicke.
Cubs manager Dale Sveum said Arrieta needs to work on putting away opposing batters when he gets ahead of the count.
"It's obviously something we're trying to get a grip on, it's been a problem, couple good pitches and get two strikes on guys and not being able to make a pitch to put somebody out," said Sveum.
Valbuena hit a two-run homer into the right-field basket in the second inning. It was his 10th of the season and first home run since July 20th. Bogusevic added a solo homer off Hellweg in the sixth to cut the Brewers lead to 4-3. It was his fourth of the season.
Cubs manager Dale Sveum said 2B Darwin Barney deserves to repeat as a Gold Glove winner. Barney had four errors and a .993 fielding percentage entering Saturday. "He hasn't done anything for anybody to take it away from him," Sveum said. "He's had a heck of a year defensively again." ... RHP Scott Baker (Tommy John surgery) will not be limited in his first outing since Sept. 24, 2011 on Sunday against the Brewers, but he likely won't throw more than 100 pitches, Sveum said. ... Brewers CF Carlos Gomez was out of the starting lineup, but came in as a pinch-hitter in the eighth and stayed in the game. Gomez has been slowed with a sore knee. ... Despite both teams competing to stay out of the cellar in the NL Central, the announced crowd was 34, 929. ... Cubs RHP Chang-Yong Lim made his major league debut in a relief appearance in the seventh. He became the 32nd player to make his Cubs debut this season, a franchise record.