"Call it what you want, man, just wasn't a good day," Garza said.
Garza (6-7) faced eight batters and got just one out, allowing four singles, a double and two walks in the shortest of his 211 regular-season big league starts dating to 2006. His previous low was 1 1/3 innings at the Marlins on June 18, 2010, according to STATS.
"He didn't throw the ball that bad," Roenicke insisted.
Garza had been 4-2 with a 2.35 ERA in his previous eight outings, but Saturday's effort caused his season ERA to rise from 3.69 to 4.04. He dropped to 0-3 with a 7.33 ERA in six career starts against the Nationals.
He was lifted after 42 pitches.
Tanner Roark (9-6) gave up one runs and six hits in seven innings with five strikeouts. In his first full season as a starter, he has allowed two earned runs or fewer in 13 of 19 outings.
"It's a lot weight off my shoulders whenever we get five runs in the first," he said.
Adam LaRoche's walked loaded the bases, and Zimmerman bounced a single up the middle for a 2-0 lead.
"I felt fine. Nothing felt off, " Garza said. "Just ... started off the game with a gem-shot single. ... Another bad break, and then Zimm hit a four-hopper up the middle."
Bryce Harper's eight-pitch walk reloaded the bases, Ian Desmond's dribbler for an infield single drove in a run and Ramos chased Garza with a two-run single. Ramos is 24 for 61 (.393) with nine RBIs in his last 17 games.
"You want to be aggressive and you've got an opportunity for a crooked number there," Williams said. "I think the big at bat there was Wilson's. He got behind, got to two strikes, and got a slider out. That's a big cushion there."
Milwaukee got a run in the second when Jonathan Lucroy doubled, stole third and scored when Ramos's throw skipped into left field for third first of two errors by the catcher.
Run-scoring singles by Ramos in the third and Zimmerman in the fourth made it 7-1 against Marco Estrada, who pitched 5 2-3 innings of relief. Zimmerman is 26 for 75 (.347) with 17 RBIs since June 24.
LaRoche added a sacrifice fly in the sixth.
NOTES: Williams said RHP Jordan Zimmermann, who left his last start in the fourth inning due to a right biceps cramp, threw a good bullpen session Saturday and is to start Tuesday at Colorado. ... Milwaukee RHP Yovani Gallardo (5-5, 3.68) opposes LHP Gio Gonzalez (6-5, 3.56) in Sunday's series finale. ... Singer Austin Mahone, on hand to perform a postgame concert, threw the ceremonial first pitch.