Santos was rewarded after the game when the Mets traded backup catcher Ramon Castro to the Chicago White Sox for right-hander Lance Broadway, ensuring the rookie will stay with the club when Brian Schneider comes off the disabled list Saturday.
Gary Sheffield led off the 11th with a single to left off Brian Sanches (1-1), who threw over to first several times to check on the aging slugger with David Wright up. After Wright struck out -- smashing his bat when he reached the dugout -- Sheffield stole second and went to third when Ronny Paulino's errant throw went into center field.
Fernando Tatis was hit by a pitch before Santos dumped Sanches' first pitch into left field to give New York its fourth consecutive win and sixth in seven games.
Pedro Feliciano (2-1) got one out to earn the win for New York, which improved to 16-8 at Citi Field.
The injured-riddled Mets welcomed All-Star center fielder Carlos Beltran back to the lineup and Schneider could return for the second game of the series. Beltran, who missed two games with a bone bruise below his right knee, went 0-for-4 but made a nice running catch on Emilio Bonifacio's sinking liner in the third before throwing to second to double off Wes Helms.
Castro's trade solves what could have been a sticky problem for New York. Santos has hit safely in 16 of his 20 starts and has 12 RBIs in his last 14 games, earning a spot on the team.
Santos, the only one of the three with minor league options, bolstered his case to stay with a leadoff drive that tied it in the fifth. He hit an 0-2 pitch from Sean West over the wall in left for his third of the season.
West pitched seven sharp innings in his second career start, yielding just four hits. The 6-foot-8 left-hander has allowed three runs in 12 innings this season but is still looking for his first major league win.
The Marlins went ahead 1-0 in the fourth but missed a chance for a bigger inning. Chris Coghlan led off with a triple to center and scored on Dan Uggla's sacrifice fly. Jorge Cantu then doubled to right and moved up on John Baker's grounder to second.
Florida put runners on first and second with two out in the eighth but Bobby Parnell retired Uggla on a bouncer to second.
New York loaded the bases with one out in the bottom half against Kiko Calero and failed to score. Calero fanned Wright before Tatis flied out to drop to 0 for 16 this season with two outs and runners in scoring position.
Pelfrey gave up one run and five hits in 7 2/3 innings for New York, continuing an impressive run but failing to beat Florida yet again. The 6-foot-7 right-hander has pitched at least six innings in each of his last five outings and is 2-1 with a 2.93 ERA in six starts this month.
Pelfrey hasn't recorded a win against the Marlins since his major league debut on July 8, 2006. He is 1-5 with a 5.36 ERA in nine career starts against them.
Marlins SS Hanley Ramirez was held out of the starting lineup with tightness in his right groin. He pinch hit in the 10th and grounded out. Ramirez left Tuesday night's 5-3 loss at Philadelphia in the third, shortly after he beat out a grounder to shortstop for an infield single. ... Marlins manager Fredi Gonzalez said utilityman Alfredo Amezaga (bruised left knee) likely won't be ready to come off the disabled list Monday when he's eligible to be activated. ... The Mets also acquired OF Emil Brown from the San Diego Padres for a player to be named. Brown and Broadway both were assigned to Triple-A Buffalo. ... Castro is owed $1,748,634 of his $2.5 million salary, and the Mets are sending the White Sox at least $1.4 million.