McDonald may have helped himself even more.
"It was a big moment for my team in the sixth and I was able to bump my chest and slow myself down and get out of that inning because I wasn't very sharp today," McDonald said.
McDonald gave up a run for the first time after 13 scoreless innings, ending the longest scoreless run by a Pirates pitcher this season.
He finished with eight strikeouts won for the third time in four starts. McDonald (5-2) held the Brewers to four hits and a walk, and only one of the three runs he allowed was earned.
"He didn't have his best stuff today but he did have, and he has for much of the season, an extremely good downhill angle on his fastball." Hurdle "It was good for him to finish."
Joel Hanrahan pitched a shaky ninth for his 14th save of the season. Brooks Conrad led off with a solo home run, and pinch-hitter George Kottaras walked before Norichika Aoki hit into a game-ending double play.
"The last at-bat, to square up a high velocity fastball, he's got to feel better," Hurdle said of Barmes, who entered the game hitting .167.
"It's tough to lose but I really do like the way we played," Brewers manager Ron Roenicke said. "I thought it was a good ballgame. They just did a little bit better job."
The Pirates took two out of three in the series for their first winning series in Milwaukee since April 2010.
"It's good to get a series win but to make it anything more than that, I'm not going to be jumping around, dancing in the streets," Hurdle said. "We expect to win series when we go on the road, just like we do at home. We know the history and it is nice to do it, I get that."
The Brewers are 59-21 against the Pirates since 2007.
McDonald led off the fifth inning with a single, and scored on McCutchen's homer. Jones later made it 4-2 Pirates by homering for the second day in a row.
Rod Barajas added a solo homer in the top of the sixth.
Brewers starter Michael Fiers (1-1) gave up four runs and eight hits with eight strikeouts and a walk in five innings in his second big league start.
Nyjer Morgan homered for the second time in three days for Milwaukee, taking McDonald deep in the sixth, after ending a streak of 138 plate appearances without a homer -- or RBI -- to start the season on Friday night.
With two outs in the first, Taylor Green hit an RBI double and Weeks singled in a run against McDonald, who struck out Ransom to end the inning.
He retired 14 straight batters before Morgan hit a solo home run with one out in the sixth inning to cut the Pirates lead to 5-3.
Morgan's solo homer in the first inning Friday night snapped his major league record of 138 consecutive plate appearances without an RBI to start a season.
Brewers slugger Ryan Braun was held out of the lineup for a second consecutive day after aggravating a right Achilles tendon injury and hurting his right hip sliding into second base on Friday night.
Braun pinch-hit for Ransom with runners on first and second in the eighth but flied out deep to right to end the inning. The Brewers were without third baseman Aramis Ramirez, who left Saturday night's game with a strained left quadriceps. Green got the start at third Sunday.
"I think everybody fought hard but I don't think you play for moral victories at this level," Braun said. "Whoever is in there we need to find a way to compete and try to win games. Certainly we played well today, just not quite well enough to get the victory."
The Brewers have used a new starting lineup in each of the last 17 games. . Casey McGehee, a member of the Brewers playoff team last year, got a start at third base for the Pirates on Sunday. . Pirates rookie first baseman Matt Hague's hitting streak ended at eight games after going 0 for 4. He had hit safely in every game in which he had played since being promoted from Triple-A Indianapolis on May 25. . Brewers pitcher Randy Wolf entered the game as a pinch runner in the ninth.