Ethier drove in the winning run when he drew a bases-loaded walk in the seventh, and he saved at least one run when he robbed Brandon Allen on a long drive to the wall one inning later.
"Him drawing the walk, him getting the catch at the wall was the difference in the game on both sides," D-backs manager A.J. Hinch said.
The loss snapped Arizona's five-game winning streak.
"It's a tough loss for us because we had plenty of opportunities on offense and on defense to change the complexion of the game," Hinch said. "Too many opportunities missed on both sides against a good team like that to win. It just felt like a game where if we had played a little bit better we would have won."
It looked like the D-backs might blow things open early when Stephen Drew and Ryan Roberts drew walks to start the game against Vicente Padilla. Justin Upton then reached on a bunt to load the bases for Mark Reynolds and Miguel Montero, two of the team's better hitters.
Instead of a big inning, though, Padilla fanned the pair swinging, and after an infield hit by Gerardo Parra scored one run, the D-backs could do no further damage.
"Bases loaded in the first, no outs, came away with a run," Hinch said. "That didn't really feel satisfactory."
It didn't take long for the Dodgers to tie the score as Matt Kemp homered in the bottom of the first off Yusmeiro Petit.
The right-hander pitched well, but the Dodgers managed to chip away at him for single runs in the second and third innings to take a 3-1 lead.
In the second, Padilla blooped a two-out single to right that second baseman Roberts caught up to, but his momentum was carrying him the wrong way and his throw to the plate was just a hair too late to get Russell Martin.
Then in the third, with Kemp on second, Ethier flied out to right, and when Upton threw the ball in, it hit Kemp, who was retreating to second base. The ball caromed away far enough for Kemp to come all the way around to score.
The D-backs managed to tie the score in the sixth when Rusty Ryal and John Hester delivered back-to-back, pinch-hit RBI singles.
"We battled and did our part to stay in there," Hinch said.
The Dodgers loaded the bases against reliever Leo Rosales with one out in the seventh thanks to a pair of walks, one of which was intentional, and a double. Southpaw Clay Zavada was summoned to face the left-handed-hitting Ethier, and he walked him to force in what proved to be the game-winner.
Unfortunately for the D-backs, Ethier was not done.
In the top of the eighth, after Ryal drew a two-out walk, Allen blasted a Ramon Troncoso offering deep to right.
"I thought I hit it pretty high and it didn't seem to be carrying too much," Allen said.
The rookie took his eyes off the ball to focus on running hard, so he did not see Ethier race to the wall and make a leaping catch.
"I was booking it," he said. "I just waited for the crowd to react."
The 45,433 on hand at Dodger Stadium roared their approval when Ethier made the catch.
"A great catch by Andre," Allen said.
In the D-backs' dugout, Hinch held out hope that somehow the ball had eluded Ethier's glove, right up until he saw Ethier show the umpire the ball as he jogged off the field.
"Off the bat I thought it was a homer," Hinch said. "He kind of came out of nowhere and made a big-time play. The Ethier catch just takes the absolute wind out of you."
Steve Gilbert is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.