Blanton (1-1) allowed eight hits but left with a 6-3 lead. He made his first start since April 23 after being sidelined with an impingement in his throwing elbow.
The Phillies won for the 18th time in their past 21 games in Miami.
While Blanton benefited from some nifty fielding, Florida had trouble catching the ball. When Jimmy Rollins homered on the game's fifth pitch, right fielder Mike Stanton leaped but the ball deflected off his glove and cleared the wall. Marlins pitcher Javier Vazquez dropped a throw covering the plate in the third, which let an unearned run score.
The Marlins' start matches the best in franchise history, but they've lost four of their past five games to fall three behind the NL East-leading Phillies (23-11), who have the best record in the majors.
Next, Florida must face reigning NL Cy Young Award winner Roy Halladay, who will pitch in Miami for the first time since last May, when he threw his perfect game. He'll be opposed Tuesday by Marlins ace Josh Johnson.
Rollins' second homer of the season set a tone, and the Phillies kept hitting. Ross Gload made his second start of the year and had a pair of RBI singles. Shane Victorino tripled to extend his hitting streak to 12 games.
Vazquez (2-3), who lasted only 4 1-3 innings, allowed nine hits and six runs, five earned.
The Phillies' Vance Worley gave up one run in three innings, and Ryan Madson pitched a scoreless ninth for his fourth save in as many chances.
Gaby Sanchez of Florida, chosen NL player of the week before the game, drove in three runs with his fifth homer and a double. Chris Coghlan had three hits and drove in a run.
The matchup between the top teams in the NL East standings failed to excite ever-apathetic South Florida. The crowd of 11,444 was the smallest to watch the Phillies this season.
Florida went ahead in the first with singles by Coghlan and Hanley Ramirez, and Sanchez's two-run double. Coghlan hit a two-out RBI single in the second to make it 3-1.
Vazquez gave up five singles and committed an error in the third, when Philadelphia scored three times to take the lead for good. Ryan Howard and Gload drove in a run each with a bases-loaded single, and a wild sequence led to the third run.
When Placido Polanco tried to score from second on Gload's hit, the throw from the outfielder was wild, and catcher John Buck retrieved the ball and tossed it to Vazquez covering the plate. Vazquez had time to tag Polanco but dropped the throw.
Victorino tripled to start the fifth and scored on Polanco's sacrifice fly, and Gload's run-scoring single made it 6-3. Gload raised his lifetime average against Vazquez to .439 (18 for 41).
NOTES: Marlins RHP Edward Mujica left in the seventh with a strained left knee. ... Philadelphia 2B Chase Utley went 1 for 7 in his second extended spring training game. "So far, so good," said the five-time All-Star, who hasn't played for the Phillies this season because of patellar tendinitis in his right knee. ... Vazquez has allowed a run in the first inning in each of his seven starts. ... Buck lost track of the count in the fourth and didn't realize he had drawn a walk.