Fans kept a close eye on the out-of-town scoreboard, cheering when the Marlins took a 2-0 lead in the first inning at Shea Stadium.
A few minutes later, Howard got them roaring when he connected to give the Phillies a 3-0 lead in the first. The sellout crowd screamed "MVP! MVP!" and waved their white-and-red "Fightin' Phils" towels in appreciation.
They went wild in the ninth after manager Charlie Manuel got into a heated argument with plate umpire Andy Fletcher and was ejected for arguing that Kory Casto had struck out. The Philly faithful gave Manuel a standing ovation and chanted his name.
Chase Utley had a three-run double and Howard drove in four runs as Philadelphia built a 7-1 lead off Collin Balester (3-7).
The Nationals chipped away against Blanton (4-0), but four relievers combined to toss three scoreless innings.
The Phillies reached 90 wins for the 12th time in the franchise's 126-year history. They hadn't done it since winning 97 games in 1993.
Blanton allowed four runs - one earned - and five hits. The right-hander was 5-12 with Oakland before joining the Phillies in a midseason trade.
Jayson Werth and Utley hit one-out singles in the first to bring up Howard. The 2006 NL MVP drove an 0-1 pitch into Philadelphia's bullpen in right-center.
Howard is batting .349 (29-for-83) with 11 homers and 32 of his major league-best 146 RBIs this month. He has raised his overall average to .250 and is making a strong push to win his second MVP award in three years, though teammate Brad Lidge deserves serious consideration.
Lidge, who is 40-for-40 in save opportunities, was chosen the Phillies' most valuable player by the local chapter of the Baseball Writers Association of America.
The Phillies chased Balester with four, two-out runs in the second inning to take a 7-1 lead.
Greg Dobbs led off with a double. Jimmy Rollins walked with two outs and Werth reached on an infield single to load the bases. Utley missed a slam by a few feet, clearing the bases with a double off the left-field wall. Howard followed with an RBI double to left.
The Nationals scored a pair of unearned runs in the fifth after Howard booted Pete Orr's grounder with one out. Emilio Bonifacio had a sacrifice fly and Cristian Guzman singled in a run to cut it to 7-3.
