MIAMI -- Bryce Harper hit a grand slam as part of a seven-run seventh inning as the Washington Nationals defeated the Miami Marlins 7-0 on Tuesday night at Marlins Park.

The Nationals (10-3), who lead the NL East, hit four home runs in their huge inning. That's the first time Washington has hit four homers in an inning since the Nationals came into existence in 2005. It's also the first time the Marlins have allowed four homers in an inning.

Adam Conley, a rookie left-hander for the Marlins (4-8), was working on a shutout before Jayson Werth pulled a 3-2 fastball for a solo homer to left-center.

Catcher Wilson Ramos homered to left-center on the next pitch. Harper's grand slam, on an 86-mph breaking pitch from reliever Chris Narveson, gave Washington a 6-0 lead.

It was Harper's seventh homer of the season and his fifth in the past six games. It was also his second grand slam in five days.

The next batter, Ryan Zimmerman, capped the inning with a solo homer.

Washington's power display overshadowed an outstanding effort by Nationals starter Stephen Strasburg (3-0), who pitched eight scoreless innings, allowing three hits and two walks. He struck out 10 and lowered his ERA to 1.25.

Strasburg also went 2-for-3 at the plate and is hitting .250.

Conley (0-1), who struck out eight and walked just one, pitched brilliantly until Werth got to him. In the first inning, Conley struck out Harper swinging at a 2-2 curveball with a runner on third and no outs. In the fourth, Conley again struck out Harper swinging, this time on a 94 mph fastball.

Ultimately, though, Conley was charged with four runs in 6 1/3 innings. Before that inning, he had pitched 12 consecutive scoreless frames over two games.

NOTES: Miami rested SS Adeiny Hechavarria and started SS Miguel Rojas. ... Marlins RHP Edwin Jackson (strained right triceps) was placed on the 15-day disabled list, retroactive to April 18. He had been pitching out of the bullpen. ... To reinforce its bullpen, Miami recalled RHP Nick Wittgren from Triple-A New Orleans. He had a 3.38 ERA in four relief appearances at New Orleans. Wittgren made his major-league debut in the seventh inning and walked the one batter he faced. ... Marlins OF Ichiro Suzuki needs one more steal to reach 500 in his career. ... Marlins manager Don Mattingly compared Nationals RF Bryce Harper with former Dodgers OF Kirk Gibson. Harper, 23, became the eighth-youngest player in major-league history to reach 100 home runs.