Ethier was the third player walked by Leo Rosales (1-1) in the seventh inning, which also included a double by Rafael Furcal.
Matt Kemp had a solo home run for Los Angeles, who won for the fifth time in its last seven games and leads the National League West by 5 ½ games.
Arizona's Justin Upton had three hits and extended his hitting streak to 10 games.
Ronald Belisario (3-3) got the win in relief of Vicente Padilla. Jonathan Broxton picked up his 30th save.
Padilla, who lasted 5 1/3 innings, drove in a run in the third inning as Los Angeles grabbed a 3-1 lead. The Diamondbacks tied it in the sixth in RBI singles by Rusty Ryal and John Hester.
Copyright 2009 by United Press International.