"This guy sat out three weeks, came back [after] a three-inning rehab, and you saw tonight, his arm strength's good, his arm strength's back," manager Terry Collins said. "Early in the game, his command was good. Just all of a sudden left some balls in the middle of the plate. But I thought he threw the ball very good."
Pitching coach Dan Warthen also agreed Santana's command and delivery were sound, though neither he, Collins nor Santana fully denied the notion of shutting him down for the season.
"It's just a matter of building that arm strength up, because we saw vintage Johan for three innings," Warthen said.
"We'll have to talk about [shutting him down], and we'll have to talk to Johan and see how the body feels, the arm feels, how he feels mentally. So I'm not going to discount anything, I'm not going to say something one way or the other. We'll all sit down and have a pow-wow."
The Mets started fast, jumping quickly on Nats left-hander Ross Detwiler in the first inning. With two outs, David Wright singled and then advanced to third on a Scott Hairston double. Two pitches later, Daniel Murphy singled up the middle to score both runners.
Hairston's double was his first of three on the night, matching the Mets' single-game record.
But after that first inning, Detwiler promptly settled down. The Mets managed only three doubles between the second inning and Detwiler's exit in the sixth. The 26-year-old left-hander improved to 7-5 after allowing three runs on six with one strikeout and one walk.
Santana's unraveling began in the fourth, and it came abruptly. Three singles, each hit hard up the middle, loaded the bases. Then, on a 1-1 count, Morse blasted a 90-mph fastball far over the right-field wall for his third-career grand slam as the crowd -- a near-sellout announced at 34,827 -- erupted.
"We tried to come up and in to Morse, and it just stayed pretty much up in the middle of the plate and he put a good swing [on it]," Santana said. "We had a plan coming in, I felt pretty good. I warmed up pretty good. I was commanding my fastball better tonight, it just came down to a couple of pitches."
In his span of five straight losses, Santana has allowed 33 runs in 19 innings while pushing his ERA from 2.76 to 4.85.
Harper's home run followed in the fifth, landing not far from where Morse's did. It came with two outs, after Jayson Werth reached on a single, further eliminating any momentum the Mets might have had left after the grand slam.
"The ball to Morse, he left out up over the plate," Collins said. "The ball to Harper was down and in, when he was going to go away. You've got to hit your spots. I think he's getting better and better at it.
"The point is, there's light at the end of the tunnel, because you know he's healthy."
Manny Acosta relieved Santana prior to the sixth and pitched two innings of one-hit, scoreless ball, striking out two batters along the way. Ramon Ramirez pitched a scoreless eighth inning.
The Mets tacked on single runs in the both the sixth and seventh innings, the final coming on Kelly Shoppach's first home run as a Met, but the Nationals' bullpen held them scoreless the rest of the way.
"All these games are big games," Werth said. "The Mets are ahead, 2-0, Johan is perfect through three, [Morse] goes big fly to make it a 4-2 game, just like that."