Espinosa, Rodriguez hit 3-run homers in Nats win
Ian Desmond also homered for the Nationals, who set season bests with eight runs and 11 hits.
Marquis (1-0) allowed two runs on nine hits in seven-plus innings. He struck out four and walked one. It was Marquis' first home win in eight tries with the Nationals.
Espinosa's second homer of the season gave the Nationals a 4-2 lead in the fifth inning. One inning later Rodriguez hit his first home run of the year, making it a five-run lead.
Yovani Gallardo (1-1) allowed seven runs on 10 hits, striking out five without a walk. Casey McGehee was 3 for 5 with an RBI for the Brewers, who dropped the first two games in the three-game series.
Saturday's game was postponed by rain, leading to the first doubleheader at Nationals Park since a twin-bill with the Giants on June 4, 2009.
Espinosa was moved to the leadoff spot on Friday, replacing the slumping Desmond. Desmond, batting sixth, started the season 0 for 29 at home before his sixth-inning double. Desmond hit his second homer of the season in the eighth.
The Brewers scored in the top of the first inning on an RBI single by McGehee, and made it 2-0 in the fourth. Milwaukee loaded the bases on singles by McGehee, Mark Kotsay and Carlos Gomez. Gallardo came up with one out and singled to right field, scoring McGehee. Marquis got out of the jam, retiring Rickie Weeks on a foul popup and getting Craig Counsell to ground out to short.
After Rick Ankiel singled in the first inning, Gallardo retired 10 consecutive batters. Jayson Werth ended that streak with a fourth-inning single to left, and Adam LaRoche followed with a single to advance Werth to third. Werth scored on Michael Morse's sacrifice fly to make the score 2-1.
Gallardo had more trouble in the fifth, giving up singles to Alex Cora and Marquis before Espinosa sent a full-count fastball into the Nationals' right field bullpen.
In the sixth inning, Morse's single and Desmond's double set up Rodriguez's homer, which just cleared the wall above the out-of-town scoreboard in right-center field.
The Brewers scored two runs after loading the bases in the ninth inning.
NOTES: Washington placed RHP Todd Coffey on the 15-day disabled list (left calf strain) retroactive to April 9 and recalled RHP Collin Balester from Triple-A Syracuse. ... The Nationals starting pitcher has lasted at least five innings in every game this season. ... Milwaukee OF Nyjer Morgan (right thigh bruise) did not start in the first game. Morgan, who was traded to the Brewers from the Nationals in March, grounded out as a pinch-hitter in the seventh inning. ... Brewers RHP Zack Greinke (fractured left rib) will travel with the team to Philadelphia, and then leave to make his first rehab start for Class-A Brevard County on Tuesday. ... Brewers OF Ryan Braun has reached base in all 14 games this season.