Beckett (1-1) and Diamondbacks rookie Tyler Skaggs engaged in a pitchers' duel over the first five innings. Ethier then broke a 1-1 deadlock with a solo homer into the left-field pavilion in the sixth against Matt Albers (0-1).
Beckett, obtained from the Boston Red Sox along with Adrian Gonzalez, Carl Crawford and Nick Punto in a blockbuster deal last week, held the D-backs to one run on six hits over 6 2/3 frames. He walked one and struck out nine.
Hanley Ramirez also homered for second-place Los Angeles, which remained 4 1/2 games behind National League West-leading San Francisco.
Skaggs, making his third major league start, finished by allowing one run on five hits over five frames.
Justin Upton went deep to provide Arizona's only run.
Notable deaths of 2014 [PHOTOS]