With two outs in the eighth and the score tied 1-1, Ethier sent a 2-0 breaking ball from Jason Grilli (0-1) four rows deep into the right field stands, marking his 30th birthday with a timely solo blast.
Javy Guerra collected his third save with a scoreless ninth and Los Angeles took its home opener while celebrating the start of its 50th year at Dodger Stadium.
Kenley Jansen (1-0) picked up the victory in relief of Clayton Kershaw, who held the Pirates to one run on four hits over seven innings.
Matt Kemp got the other RBI for Los Angeles, which improved to 4-1.
Kevin Correia got a hard-luck no-decision for Pittsburgh, yielding one run on four hits through six frames.
Matt Hague drove in the Pirates' only run.