Howard's slam traveled 475 feet and became only the second ball to reach the third deck in right field. He also added a solo homer to lead the Philadelphia Phillies to a 9-6 victory over the Washington Nationals on Saturday night.
Trailing 3-2 in the third, Howard connected on his slam to move past Hall of Famer Mike Schmidt. Howard had given the Phillies their first run with a solo shot in the second inning. It was the 19th multihomer game of Howard's career.
"Yeah, it definitely felt good," Howard said of his grand slam. "I knew it was high enough to go out. When everything comes together, you never know how far it's going to go. I got it pretty square."
Howard also hit the only other homer to reach the third deck in the ballpark's five-year history off the Yankees' Mike Mussina on June 20, 2006.
"He's just as strong as anyone," Phillies manager Charlie Manuel said, when asked to compare Howard to the all-time sluggers. "I've seen him hit some long ones."
Cole Hamels (3-2) gave up six runs and eight hits in six innings for the win. He struck out seven in his worst start this season since allowing seven against Colorado to open the season.
"I pitched pretty bad and made a lot of mistakes," Hamels said. "They're a good hitting team and you can't make mistakes and can't take them lightly."
Hamels was appreciative of the run support and spoke glowingly of Howard.
"Our offense is very potent and when they're able to get big hits and score runs it really does help, especially when I'm not able to hold my own," he said.
On Howard, Hamels said, "It's impressive how strong he is. He's the power."
Brad Lidge pitched a scoreless ninth for his 11th save.
Shairon Martis (5-1) lost for the first time in 10 starts for Washington. He surrendered seven runs and seven hits in four innings. Howard has plagued Martis in his career hitting three homers and driving in nine runs in seven at-bats.
"It's tough losing so much, but we're not going to quit," Nationals manager Manny Acta said. "We'll come back tomorrow and play hard."
Pinch-hitter Ronnie Belliard hit a two-run homer to left in the sixth to pull Washington to 7-6. But Philadelphia tacked on a pair of runs in the bottom of the inning when Anderson Hernandez booted Howard's grounder to second with the bases loaded.
The Nationals took a 3-0 lead in the second with three hits, as Will Nieves drove in two with a double and Hernandez one with a single.
"We're just very inconsistent and that's why our record is what it is," said Washington right fielder Adam Dunn, who made two errors to give him seven for the season.
Prior to the game, the Nationals recalled Gonzalez from Triple-A Syracuse and optioned outfielder Justin Maxwell to Syracuse. Gonzalez, who batted .311 in 23 games with Syracuse, went 2-for-3 with a run and an RBI Saturday. Gonzalez was filling in at shortstop for Cristian Guzman, who got the night off to rest a jammed right thumb. Chase Utley was hit by a pitch in the eighth inning, his major league leading 11th hit by pitch this season. The Phillies announced after the game that Antonio Bastardo will take Brett Myers' spot in the rotation Tuesday in San Diego. The left-hander is 3-2 with a 1.89 ERA in 11 games between Double-A Reading and Triple-A Lehigh Valley this season. Myers will have hip surgery next week that likely will end his season.