When the Cardinals' Brendan Ryan led off the bottom of the eighth in a tie game with a drive right at him, Murphy broke in, then back and had the ball lined up. But as he stepped back, Murphy slipped and fell, allowing the ball to fly over his head and Ryan to end up at third with a triple.
Ryan then scored the winning run on a Rick Ankiel double, and the Cardinals added an insurance run and beat the Mets, 6-4, on Tuesday night at Busch Stadium.
"I actually felt like I did everything right on that ball," Murphy said. "I slipped. I don't really know how to explain it. I thought I was right there. It would have hit me in the chest. I just slipped."
It's the second time in the first 13 games of the season that Murphy has misplayed a ball that cost his team a win. The former Minor League infielder dropped a ball in left that led to both Marlins runs in a 2-1 loss at Florida on April 12.
"I'm a little concerned, I have to be honest with you," said Mets manager Jerry Manuel said. "He's a hard worker. He does everything we asked him to do. I think for the most part, I'd just like to see him relax. That's all, just relax.
"We just have to slow him down a little bit. He has to relax a little bit more than he is right now. It seems like he is playing a little tight. We have to find a way to get him comfortable, and I think he will continue to work and head in that direction."
The Mets almost took the lead in the top of the eighth when center fielder Carlos Beltran tried to score from third after advancing there on a flyout to right field.
The throw to third bounced out of Joe Thurston's glove as he attempted to make the tag and rolled toward the pitcher's mound. But with the pitcher backing up the play and nobody near the mound, Beltran raced home and tried to score the go-ahead run. Thurston chased down the ball, barehanded it and fired to catcher Yadier Molina at the plate.
Beltran didn't slide, his foot stepped right on top of Molina's and he missed the plate and was tagged out to end the inning.
"I didn't realize how close I was to home plate," Beltran said. "I was watching the ball and when I looked at home plate, I was too close to slide. Molina was on top of the plate and I tried to go over his foot, but I stepped on it and I wasn't able to touch [the plate]."
Beltran's out at home was one of three Mets outs on the basepaths. Murphy was picked off by Molina in the first inning when he wandered too far off of first base with David Wright at the plate, and he was also thrown out at home in the fourth inning when he attempted to score on a grounder to first baseman Albert Pujols.
Starter Oliver Perez was given a 4-0 lead and kept the Cardinals scoreless for four innings before running into trouble in the fifth. A leadoff hit by pitcher Todd Wellemeyer was followed by an Ankiel single and a Pujols two-run double that cut the lead in half. After a walk and a single, Perez issued a bases-loaded walk to shortstop Khalil Greene to make the score 4-3 and chase him from the game.
"I thought he was trying to kind of paddle all night," Manuel said of Perez. "He was walking the tight rope. I was trying to give him every opportunity to get through that fifth inning, but I think a leadoff hit to the pitcher was kind of the beginning of the undoing for him at that point. You want your guy to finish that inning off, and you give him every opportunity to do that, but it just didn't work out."
Casey Fossum replaced Perez with the bases loaded and made his first appearance with the Mets after being called up from Triple-A Buffalo, but he walked Thurston on four pitches to tie the game. Thurston had been called out on strikes with the bases loaded against Perez in his previous at-bat in the fourth inning.
The Mets left six runners on base, including two in both the first and second innings, and had two runners thrown out at home plate. Carlos Delgado appeared to have a chance to score on a double by Beltran in the first, but he stopped at third and was unable to score.
"We had a four-run lead and we didn't add on to that," Manuel said. "I think we have enough offense to where we should be able to add a run here or there, but we weren't able to do that.
"We had a chance to do some things."
But even with the miscues on offense, the Mets still sat tied 4-4 in the eighth with a chance to win the game before Murphy's slip.
"This one is tough to swallow because we lost the ballgame," Murphy said. "I really felt like I put myself in position to make the play. I just slipped."
B.J. Rains is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.