Greinke only made two starts before it was discovered that he had a broken rib, sustained during a pickup basketball game. Marcum was shut down for nearly two weeks after experiencing shoulder tightness in a start against the Chicago White Sox on March 17.
Many of the team's fears were eased on Monday when Marcum returned.
Marcum will be throwing a bullpen session on Wednesday as he prepares for his first start of the regular season Saturday against the Reds in Cincinnati. The Brewers will open against the Reds on Thursday with Gallardo on the mound, then have Friday off.
"There was none of the tightness I had before and the ball was coming out of my hand pretty good," said Marcum, who was 13-8 for Toronto in 2010. "I felt good, except for the home runs The first 50 pitches, I felt good, then I got tired.
"I wasn't really worried about the shoulder," he said. "A lot of people go through tightness and soreness early in the spring."
Brewers first-year manager Ron Roenicke said he felt a bit uneasy about Marcum after the pitcher's initial discomfort, but felt much better recently after watching Marcum throw a bullpen session.
"I don't think his location was where it normally is, but he got in the work," Roenicke said. "He still made some pretty good pitches up in the zone. It is kind of a relief when you see him out there. You never know until he gets in the game."
Roenicke also saw the debut of right-hander Sergio Mitre, acquired in a trade on March 25 from the New York Yankees for outfielder Chris Dickerson. Mitre is expected to be used as a starter and a long reliever.
Mitre entered the game in the top of the fifth and promptly walked the first hitter, Cedric Hunter, on four pitches. He got Kyle Blanks to hit into a double play, but gave up Venable's second homer of the game as the Padres cut the lead to 5-4.
"He was a little inconsistent with those four straight balls," Roenicke said. "He usually throws a really nice sinker. He can be tough to hit."
Mitre pitched 2 2/3 innings, giving up three hits, walking two and striking out one. It had been nearly a week (March 22) since he pitched in a game for the Yankees.
"I felt good, but it felt different, in a different uniform," Mitre said. "I am just trying to get in the flow of things. It is good to get that first one out of the way."
Brewers LHP Zach Braddock pitched 1 1/3 hitless innings after being stung by a scorpion at his home on Saturday. ... The team was still waiting for the arrival of OF Nyjer Morgan after getting him in a trade with Washington on Sunday. ... Takashi Saito pitched an inning for the save. ... Hawpe, expected to be the primary 1B for the Padres, had a pair of hits to raise his average to .366.