Blanks staked the Padres to 1-0 lead with an RBI triple in the second and then, after Juan Guzman, Orlando Hudson and Will Venable had reached base with two outs, capped a six-run seventh with a bases-loader homer.
Rob Johnson drove in three runs with a two-run double and a sacrifice fly, and Hudson finished 3-for-5 with three runs scored for San Diego, which clinched its three-game series in Pittsburgh.
Cory Luebke (4-6) tossed seven innings of one-run ball, yielding no walks and striking out nine to earn the victory.
Paul Maholm (6-12) was pounded for seven runs on 10 hits over 6 2/3 innings for the Pirates, who dropped to nine games out of first in the National League Central after leading the division less than two weeks ago.
The Pirates have been outscored 28-7 over the first two games of the San Diego series.