A sudden injury has left the Braves fearing they've lost their good-luck starter.
The right-handed Medlen left the game in the fifth inning after hurting the ulnar collateral ligament in his pitching elbow. He will have an MRI exam on Thursday.
Medlen said he had no pain in the elbow before throwing a pitch wide of the plate to Jose Reyes in the fifth inning.
"It was just that pitch," Medlen said. "I felt a little tightness in my elbow. It's still pretty tight so we'll see tomorrow. ... Anytime it's your career, anytime anything goes wrong with your arm you're a little worried."
The Braves are 13-1 in Medlen's 14 starts, including 11 straight wins. He gave up four hits and two runs in 4 1/3 innings before the injury.
"He couldn't throw another pitch so, obviously, something popped in there," said Braves manager Bobby Cox. "That's my opinion. I'm no doctor."
Cox said the Braves would immediately make plans for a roster move.
"It always feels good to go back-to-back," McCann said. "It gave us the lead back and we didn't look back after that."
"When you make mistakes against that team, they make you pay for it," Pelfrey said.
The NL East-leading Braves won two of three from the Mets after losing three straight series.
The Mets, who won Tuesday night, have not won consecutive games since June 22-23. They have not won a road series against an NL opponent this season.
The loss of Medlen would be a blow to the Braves' hopes of holding off Philadelphia in the NL East. He has been one of Atlanta's most effective starters after taking over the No. 5 spot in the rotation from Kenshin Kawakami.
Kawakami has appeared in only one game in relief since his last start on June 26. Cox said Kawakami may not be ready to start if the Braves must replace Medlen.
McCann had run-scoring doubles in the first and fifth innings. The All-Star catcher has six homers and 23 RBIs since July 3.
"I've been seeing the ball well and I put together some good at-bats tonight," McCann said. "I was happy with the results."
The Braves scored four unearned runs on four New York errors, including two errant throws by shortstop Jose Reyes. Three errors came when the Braves scored two unearned runs off Hisanori Takahashi in the sixth.
"That was bad," said Mets manager Jerry Manuel. "We didn't play very well. We're a better team than that. We have to get back on track and play defense."
Wright's error came after fielding a bases-loaded grounder by Jones. Reliever Mike Dunn, who reached on Reyes' second error, scored on Jones' grounder. Wright's wild throw to second allowed Omar Infante, who reached on a single, to score from second.
"You can't kick the ball around like that," Manuel said. "... I was shocked that we played this way on defense. It's a good thing that we have a day off."
Dunn (1-0) gave up two walks in 1 2/3 scoreless innings in his first major league win.
New York's Luis Castillo had two hits, including a run-scoring single in the second. Reyes doubled and scored on a groundout by Carlos Beltran in the third.
Pelfrey gave up eight hits and five runs, three earned, in 4 2/3 innings while losing for the fourth straight time.
"I have to step up and be a lot better," Pelfrey said. "I take full responsibility for the game.
"Every start has been the same way. It's been frustrating the last six or seven starts, and that definitely continued tonight."
- The Mets' four errors were their high since their five against the Dodgers on May 18, 2009. Their last three-error inning came on June 26, 2009, against the Yankees.
- Braves LHP Eric O'Flaherty, recovering from mononucleosis, threw on the side and is expected to throw in the bullpen on Thursday.
- The Mets are 0-6 in decisive third games of series on the road, and 4-11 overall.