Marcum allowed three hits over seven shutout innings to lead the Milwaukee Brewers to a 5-0 victory against the Astros on Friday night.
"It's [flu] been going around the clubhouse, we've just got to keep doing our jobs," Marcum said. "My legs were like jelly. I threw a lot of curveballs to keep them off-balance. I didn't locate my fastball very well."
Marcum (3-1) allowed four runs and two homers in his last start against Houston but didn't permit a runner past second base this time out. He struck out six and walked two.
"He wasn't feeling all that good," Brewers manager Ron Roenicke said. "He said no big deal and his location was great, he was down in the zone most of the day, the changeup great again and the breaking ball really good."
The Brewers jumped on Brett Myers (1-1) early. Ryan Braun hit his 10th homer on a 2-1 pitch over leaping center fielder Michael Bourn in the first inning. Two pitches later, Prince Fielder launched a 450-foot homer to right.
"When you can achieve personal goals, it's great and when you help the team win it's even better," Fielder said. "You are doing your job and it means something."
It was Fielder's fifth of the season and the ninth-longest homer in Minute Maid Park history.
"That's great but it still counts as only one," Fielder said.
Myers pitched six innings, allowed five hits and four earned runs, and he walked three and struck out eight.
"I feel like if I strike out eight guys, I shouldn't give up four runs," Myers said. "It was a tough night, but you have to battle through it. I felt I made pretty good pitches. My slider wasn't as sharp early on, but I realized that later and started throwing more changeups and curveballs and was able to get through six.
"But honestly, for me, if I punch out eight guys I shouldn't give up four runs, because that means my stuff is good that day," he said.
Yuniesky Betancourt hit his first homer of the season for Milwaukee in the fourth.
Fielder doubled in his 25th RBI of the season in the third to make it 3-0 and Braun knocked in his 23rd run with a single in the seventh against reliever Mark Melancon to put Milwaukee up 5-0.
Marcum, who was acquired in a trade with Toronto in the offseason, lowered his ERA to 2.21.
Myers lost at home for the first time as an Astros pitcher. He was 9-0 in 16 previous starts.
"If you look at his numbers, it was five hits and eight strikeouts," Astros manager Brad Mills said of Myers. "Obviously the three home runs hurt, and their guy pitched pretty well. The offense wasn't there and that was about it."
Braun has reached base safely in all 25 games this season, adding to his franchise record. Robin Yount had the old record of 23.
The Astros had runners at first and second with one out in the fourth and failed to score.
Astros first baseman Brett Wallace left the game after the seventh inning with a right hip pointer following a collision with Fielder. His condition was listed as day to day.
"Honestly the biggest thing is to come in tomorrow and get some treatment," Wallace said. "I think I should be good to go. That's obviously in his [Mills'] hands as far as what he decides to do, but I think I'll be good to go."
Fielder needs three home runs to reach 200 for his career. He is fifth on the Brewers' career homer list. ... Clint Barmes was activated form the disabled list Thursday night and started at shortstop. Barmes broke his left hand when hit by a pitch in spring training. He hit .400 in four minor league games this week. ... Houston has won six of its last eight home games against the Brewers. ... Bourn's first inning stolen base gives him 18 attempts in a row without being caught, dating back to last season. ... Wallace extended his hitting streak to nine games with a first-inning single and then stole a base for the first time in his career.