NEW YORK (AP) -- One moment, Felix Hernandez was rounding the bases in glee after hitting the first grand slam by an American League pitcher in 37 years.
A few innings later, he was spiking his cap to the ground in frustration after being injured.
Hernandez hit a stunning grand slam off Johan Santana, then departed with a sprained ankle before he could qualify for a win in the Seattle Mariners' 5-2 victory over the New York Mets on Monday night.
Facing a fellow ace from Venezuela, Hernandez connected off Santana (7-6) with two outs in the second inning to give Seattle a 4-0 lead.
"My approach? Just swing. I closed my eyes," said Hernandez, who figured it was his first home run since Little League. "I was happy and I was thinking that's all I need -- four runs."
The opposite-field shot to right-center was the first home run by a pitcher in Mariners history, and the first slam by an AL hurler since Cleveland's Steve Dunning went deep against Oakland's Diego Segui on May 11, 1971, according to the Elias Sports Bureau.
"He had a pretty good swing," Santana said. "The pitch was out of the strike zone, it was up like it was supposed to be, and all of a sudden the ball leaves the park. There's nothing you can do about it."
Three innings later, Hernandez sprained his left ankle while covering home plate on a run-scoring wild pitch. Carlos Beltran slid hard into the feet of Hernandez, who left the game one out short of being eligible for a win. After trying a painful warmup pitch, he had to be helped to the dugout by team trainers.
Later, Beltran said he called Hernandez to check on him.
"It happened so fast," Beltran said. "I wasn't really watching anything except home plate. After I watched the replay, I saw that he was blocking the plate and I caught him with my spikes."
X-rays were negative and Hernandez expects to make his next scheduled start.
"Sure, I'll be there," he said.
Roy Corcoran relieved Hernandez and worked 1 1/3 hitless innings. Ryan Rowland-Smith (2-1) struck out three in two perfect innings, and Arthur Rhodes earned his first save since 2006 with Philadelphia.
Jose Lopez added a run-scoring single for the Mariners, who improved to 12-25 on the road and 2-2 since manager Jim Riggleman replaced the fired John McLaren.
The Mets fell to 3-3 under interim skipper Jerry Manuel, who managed his first game at Shea Stadium since taking over when Willie Randolph was fired last week.
"We will definitely have to make some adjustments offensively," Manuel said.
Santana allowed five runs -- one earned -- and seven hits in seven innings. It was his third loss in 16 starts with New York when giving up one earned run.
The Mets have dropped his last four outings, and the two-time Cy Young Award winner is 0-3 in that span.
"I felt better tonight than I felt for the whole season," Santana said. "We didn't execute the way we're supposed to."
Just before Hernandez homered, an error by third baseman David Wright extended the second inning. Wright also grounded into an inning-ending double play and struck out looking.
Manuel said Wright appears tired and won't start Tuesday night. Wright is the only major leaguer to play every inning this season, though he made one start as a designated hitter.
"Jerry knows the game. I'll get a blow and hopefully come back refreshed," Wright said.
In the second, the 6-foot-3, 230-pound Hernandez took a healthy hack at the first pitch he saw from Santana and clapped his hands while rounding first base. The home run came in Hernandez's first plate appearance this season and made him 2-for-9 with five RBIs and six strikeouts in his major league career.
"We were all so pumped up," Rowland-Smith said.
His next time up, Hernandez dropped down a sacrifice bunt.
"I couldn't believe that. I'll have to talk to Riggleman about that," Manuel said. "Why is this guy bunting? He just hit a home run."
Hernandez threw 51 pitches in 4 2/3 innings. The 22-year-old right-hander, who entered 4-0 with a 0.95 ERA in his previous four starts, allowed one run and two hits.
The last NL pitcher to hit a grand slam also did it at Shea Stadium. Dontrelle Willis, then with Florida, accomplished the feat on July 7, 2006.
Mariners LHP Erik Bedard was scratched from his scheduled start Wednesday against the Mets after leaving Friday's outing with back spasms. Miguel Batista will start instead. ... RF Ryan Church, on the DL due to post-concussion syndrome, could begin a rehab assignment with Class-A Brooklyn this week and return to New York's lineup this weekend against the Yankees.