Following five poor starts after coming off the disabled list, Marcum has posted two straight quality starts in a row, including a win against the first-place Reds on Wednesday.
Marcum held the Reds to one run on four hits in six innings of work, striking out seven for his first win since June 8.
"Great. Awesome. Vintage Shaun Marcum," catcher Jonathan Lucroy said after the game. "He made pitches in big situations, got some strikeouts in big situations. It was very impressive."
He won't have greater goals to play for as the Brewers were eliminated from the playoff race with their 7-0 loss to the Astros on Sunday.
"It was amazing, the run that we went on to get into contention," left fielder Ryan Braun said. "I think that we're all proud of that. Ultimately, we're disappointed we didn't end up back in the postseason, but it certainly wasn't for a lack of effort."
Marcum will take on the Padres' Clayton Richard, who will be fighting for personal goals as well Monday.
Richard is getting his second go at win No. 15 on the year, which would mark his career-best. He is coming off a rough outing his last time out, giving up four earned runs on 10 hits in 3 2/3 innings against the Dodgers.
"That was a tough one," Richard said. "You hate putting your team in that type of hole. I made pitches and they didn't work out, and of course I didn't make some pitches and they took advantage. It was a rough day."
Monday will be Richard's 33rd start of the season, which also ties his career-high set in 2010.
Padres: Volquez leaves early with injury
Padres starter Edinson Volquez exited Sunday's game against the Giants in the fifth inning with an undisclosed injury.
Volquez threw one pitch in the fifth before being pulled. He stepped off the mound and called for manager Bud Black and the team trainer to talk.
Brad Boxberger replaced Volquez, who had allowed two runs on six hits while walking three through 71 pitches.
Yasmani Grandal made his 50th start of the season at catcher on Sunday, marking the third different Padre to make 50 or more starts behind the plate this season, along with Nick Hundley (56) and John Baker (51).
According to Elias Sports Bureau, no Major League team since 1900 has had three players make 50 or more starts at catcher in the same season.
Brewers: Narveson returns to the mound
Chris Narveson got his first action back on the mound since shoulder surgery five months ago.
Narveson, who underwent season-ending surgery on his left rotator cuff on May 1, took to the bullpen mound at Miller Park on Sunday morning, throwing 20 pitches, all fastballs.
"It felt great," Narveson said. "It's a long time coming, that you come to the field with a smile on your face, ready to get back after it."
Narveson, who is slated for another bullpen session Wednesday, will head home to North Carolina to continue his rehab before heading to Maryvale Baseball Park to ramp up the rehab with coach Rick Kranitz.
The Brewers may be eliminated from the playoffs, but they still have something to play for this season.
At 81-78, the Brewers can still finish the season with a winning record, despite being 12 games under .500 as recently as Aug. 20.
"When you consider everything we went through -- the injuries, the trades, where were at a month ago -- to finish over .500 is an accomplishment, for sure," Braun said.
The Padres are now 42-39 at home, marking the seventh time in nine seasons they have a winning record at Petco Park.
Brewers manager Ron Roenicke hinted that some nicked up players may be left out of the lineup in the team's final series of the season.
"There's going to be some guys that I talk to, to see who we put back out there again [on Monday]," Roenicke said. "Corey [Hart] is definitely one of them, whether he wants to keep doing this. He's playing hurt every day and I'm not sure if he wants to keep doing that." Hart has some pain in his left foot, and players like Braun (groin) and Aramis Ramirez (wrist) have also been playing with some nagging issues.