Jonathan Broxton (2-0) blew the save opportunity by allowing four hits and two runs in top of the ninth inning, but Ethier came through against LaTroy Hawkins (0-3) with his second career grand slam. Ethier, who has 10 homers this year, had his sixth career walk-off home run.
James Loney knocked in a run in his sixth straight game for the Dodgers, who won for the fourth time in six contests.
Rookie John Ely pitched into the seventh inning and was in line for his first major league win before Milwaukee rallied in the top of the ninth. Ely, pitching a week prior to his 24th birthday, scattered four hits and gave up one run while fanning seven. The right-hander, making his first appearance at Dodger Stadium after making his big league debut last week at New York's Citi Field, didn't walk a batter. He retired 16 batters in a row at one point.
"Ely pitched a great game. He had a good changeup," Brewers manager Ken Macha said. "He didn't walk anybody. Our guys battled back. It's too bad we couldn't get the job done. As soon as Andre hit it, I headed for the clubhouse."
Dave Bush surrendered four hits and three runs -- one earned -- over five frames in the start for Milwaukee, which got two RBI from Gregg Zaun.
The Brewers won the first two games by a combined 22-9 count, but came down to the ninth inning trailing 3-1 before tying the game.
Broxton fanned Jim Edmonds to start the ninth, but Ryan Braun and Prince Fielder singled to put runners at the corners. Casey McGehee flied out to center, but Braun remained at third. Zaun then singled to left field for a 3-2 game. Pinch-hitter Craig Counsell then bounced a ball up the middle and off the glove of a diving Jamey Carroll at shortstop. The ball hit off the foot of a diving second baseman Blake DeWitt, as Fielder scored easily.
In the bottom half, Carroll singled to left field, and with one out Xavier Paul singled. Runners were at the corners after Hawkins uncorked a pitch in the dirt. Matt Kemp walked to set the stage for Ethier, who blasted a ball barely over the wall in center field for the 11th walk-off hit of his career. He had four walk-off homers last year, tying a major league record for one season.
"I want to go up there in that situation, I want to end the game right there," Ethier said. "He threw me a fastball right down the middle. I just put an easy swing on it and it just kept going."
Loney's sacrifice fly in the first scored Paul, and the Dodgers moved to a 3-0 lead in the second. Carroll doubled and scored on McGehee's error on a ball hit by Ely. Paul doubled in Ely in the next at-bat.
The Dodgers wasted a bases-loaded chance in the sixth and the Brewers got their first run in the seventh when Fielder scored on Zaun's base hit to center.
The Dodgers host Colorado this weekend, while the Brewers play in Arizona...The Brewers are 10-1 this season when scoring first and 2-15 when the opponent scores first.