Each knocked in a run during the Nationals' seven-run third inning, during which they banged out seven hits while sending 12 men to the plate.
Espinoza later added a two-run homer and scored three times, while Kurt Suzuki capped the big inning with a bases-clearing double as National League East-leading Washington took the opener of a three-game set.
Ryan Zimmerman and Steve Lombardozzi provided three hits apiece in the one-sided triumph.
Gio Gonzalez (15-6) earned the victory, allowing two runs on six hits over 6 2/3 innings. The left-hander walked a pair and struck out four.
Giants starter Ryan Vogelsong (10-6) was pounded for eight runs on nine hits after lasting just 2 2/3 innings.
Brandon Crawford drove in two runs for San Francisco, which slipped into a first-place tie with the Los Angeles Dodgers in the National League West with the loss.