PHOENIX -- The New York Mets are struggling out West, no one more than Mike Pelfrey.
The right-hander lasted just 1 1/3 innings in the shortest outing of his career and the Arizona Diamondbacks went on to rout the Mets 13-2 on Monday night.
Mark Reynolds led the Diamondbacks' barrage with an RBI triple and three-run homer, his 21st of the season.
Mets manager Jerry Manuel said Pelfrey needs to go back to the fastball that got him off to a 9-1 start. In his last six starts, Pelfrey is 1-4 with a 9.11 ERA.
"We're talking about a young man that we felt was an All-Star pitcher," Manuel said. "To have those outings that he's had here lately, that's really discouraging. He's a guy that we're counting very heavily down the stretch here to do what we need to do."
The Mets have lost four of their first five on an 11-game post-All-Star break trip to the West and seven of nine overall. They fell 5½ games behind idle Atlanta in the NL East.
Pelfrey (10-5) threw 74 pitches, 51 in a miserable first inning. He allowed six runs and seven hits.
The problem, Manuel said, is all in Pelfrey's head, and he said talked to him about regaining trust in his power pitch.
"He's not a finesse pitcher, he's not a trick guy," Manuel said. "He's a power, sinker guy, and that's what he's got to get back to."
Catcher Rod Barajas said that when Pelfrey throws the fastball lately, it's either out of the strike zone or right over the plate.
Barajas said he could be losing confidence.
"When you do struggle, doubt comes into the back of your mind. Now you're not too sure about your ability and your chances to go out there and make good quality pitches," Barajas said. "I'm not in Mike's head, but that definitely could be a factor."
Pelfry said he's fine physically. Mentally, it's another matter.
"I'm just going through one of the worst stretches of my life," he said.
Pelfry agreed that somewhere a few starts ago he got away from the fastball.
"I don't know why," he said. "I've got to get back to it."
Justin Upton had two RBI with a double and triple as Arizona amassed a season-high 18 hits.
"This is where we want to be," interim manager Kirk Gibson said. "This is who we want to be. Store that."
Ian Kennedy (5-7) gave up a run and four hits through five innings to win his second straight decision after losing his previous four.
Seven players had at least one RBI for the Diamondbacks, who were coming off a three-game sweep at the hands of the Padres in San Diego. Mets shortstop Jose Reyes committed two errors in the first two innings. The Diamondbacks' Chris Young had three leadoff singles and scored on all of them.
Reynolds, whose average had dipped to .215 entering the game, connected with the kind of power he shows when he's at his best.
"I put up a good at-bat my first at-bat and got a good pitch to hit," he said. "It is a game of confidence and it got me rolling a little bit and it carried on all night."
Arizona sent nine to the plate in the first. Johnson's double brought Young home, then Upton walked. Miguel Montero grounded to first, where Ike Davis fielded it and threw to second for the force. But Reyes' return throw to first for what could have been a double play was wild, allowing Johnson to score.
With two outs, Reynolds hit one above the 407-foot sign in straightaway center for an RBI triple to make it 3-0. Stephen Drew walked, then Gerardo Parra singled Reynolds home.
Young started the second with another single, then scored when Upton doubled. Montero, 3 for 5 with a double and an RBI, singled to put runners at first and third, bringing an end to Pelfry's night. Adam LaRoche, who had three hits, singled in a run off reliever Raul Valdes to make it 6-0.
Arizona added five runs off reliever Fernando Nieve in the sixth, three on Reynolds' shot to the upper deck in left field.
Mets 2B Luis Castillo was 2 for 4 in his return to the lineup for the first time since going on the 15-day DL on June 5 with a bruised right heel. ... Pelfrey has given up at least one run in the first inning in each of his last eight starts after doing so once in his first 11. ... Pelfrey's previous shortest outing was three innings, twice, the most recent on July 7, 2009. ... Arizona's previous season-best was 15 hits.