Michael Morse belted a grand slam and Bryce Harper added a two-run homer as the Washington Nationals edged the New York Mets, 6-4, in the opener of a three-game series.
Ross Detwiler (7-5) threw six quality innings, allowing three runs on six hits for Washington, which was coming off a successful 8-2 road trip.
Johan Santana (6-9) tumbled to a fifth straight loss after surrendering six runs on seven hits over five innings.
"It just came down to a couple of pitches," Santana said.
Santana, who lasted a career low-tying 1 1/3 innings in his previous start, retired the first nine batters after being staked to a lead on Daniel Murphy's two-run single in the first frame.
But the Nationals, perhaps sluggish following just their second off day since the All-Star break, woke up in the fourth with three straight singles by Jayson Werth, Harper and Ryan Zimmerman.
Morse, hitless in his previous nine at-bats against Santana, made it four hits in a row when he went the other way with a letter-high fastball and found the right-field seats for the Nationals' first grand slam of the season.
"It was awesome. Everyone in the dugout and in the stands was going crazy," said Detwiler of the grand slam.
Harper made it 6-2 an inning later as Werth singled with two-away prior to the rookie's 11th homer of the year.
The Mets scored a run in each of their next two turns at the plate to stay close. Scott Hairston led off the sixth with his third double of the game and eventually scored on Ronny Cedeno's groundout.
Kelly Shoppach, in his second game with the Mets since being claimed off waivers, took Craig Stammen deep to left leading off the seventh for his first National League homer to cut the deficit to 6-4.
David Wright then opened the away eighth with a single to keep hope alive, but he was erased when Drew Storen induced Hairston to ground into a rally-killing 5-4-3 double play.
Tyler Clippard put the tying run on base with a pair of walks in the ninth, but the Nationals closer got Ruben Tejada on a routine flyout to left to secure his 26th save.
Nationals shortstop Ian Desmond was activated from the disabled list before the game and went 0-for-4. He had been out since July 21 with a torn left oblique muscle ... Morse is riding a 13-game hitting streak ... The Nationals are 10-3 against New York so far this season ... Washington is 23-5 in games started by opposing left-handed starters ... Santana has pitched to a 15.63 ERA since his last win on June 30.