Both home runs came off Mets’ pitcher Johan Santana (6-9), who surrendered six runs on seven hits and struck out four in five innings at Nationals Park in Washington D.C.
Morse’s grand slam in the fourth inning, the first of the season for Washington, gave the Nationals a 4-2 advantage.
“It was awesome,” winning pitcher Ross Detwiler said. “Everyone in the dugout and in the stands was going crazy.”
Harper’s two-run homer in the fifth widened the lead to 6-2.
Detwiler (7-5) allowed three runs on six hits and struck out one in six innings for the Nationals. Tyler Clippard got his 26th save after walking two and striking out two in the ninth inning.
Daniel Murphy hit a two-run single to give the Mets a 2-0 lead in the first inning. Ronny Cedeno drove home Scott Hairston in the sixth and Kelly Shoppach homered in the seventh to narrow the gap to a two-run deficit.
The Mets (56-63) are in third place in the five-team NL East, 18 games behind the Nationals (74-45).
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