Blanks crushed a ball into the second deck in left field to put the Padres ahead to stay 3-2 in the fourth inning. The 6-foot-6 Blanks also made a running catch to rob Gaby Sanchez of an extra- base hit in the fifth inning.
The Padres handed Florida its 13th loss in 15 games. San Diego won fifth straight over the Marlins this season, outscoring them 30-10.
Wade LeBlanc (2-2) had a shaky outing but the bullpen held the Marlins in check to give San Diego its fourth win in six games after dropping four of the previous six.
Blanks' towering shot off Chris Volstad (5-10) was his fourth. Volstad has allowed 20 homers in 22 starts this season.
San Diego's five relievers allowed two hits over the final 3 2-3 innings to secure the win. Heath Bell pitched the ninth for this 34th save in 37 chances.
Erik Hamren relieved LeBlanc in the sixth inning with the bases loaded and one out. The rookie right-hander struck out pinch-hitter Mike Stanton, who was a late scratch from the lineup with a sore left big toe. He walked Emilio Bonifacio to force in a run and cut the lead to 4-3. But Hamren struck out Sanchez to escape further damage.
Jose Lopez had three doubles to tie a Marlins record and drove in a run in the first inning. Volstad added an RBI double in the fourth. Florida stranded 12 base runners.
San Diego scored in the first after Will Venable led off with a walk, stole second and scored on Cameron Maybin's single. The Marlins have allowed eight first-inning runs in their last three games.
LeBlanc won his second straight start after having gone eight starts without a win, dating back to last August. The lefty allowed three runs on six hits over 5 1-3 innings. He walked four and struck out three.
Volstad lasted five innings after giving up four runs on six hits with seven strikeouts and one walk.
NOTES: San Diego has hit a major league-low 69 home runs. ... Stanton hurt his left big toe Thursday night when he jammed it against the right-field wall while chasing Nick Hundley's triple. ... Petco Park sported two large logos in foul territory down the first and third base lines in commemoration of Sunday's retirement ceremony for Trevor Hoffman, baseball's all-time save leader. ... Marlins RHP Edward Mujica pitched for the first time since Monday night when he left with a sore right lat muscle. ... Florida RHP Clay Hensley (1-4, 4.53 ERA) will make his first start and third appearance against his former team when he faces Padres RHP Aaron Harang (11-3, 4.08), who is 6-1 over his last 13 starts.