"I don't know what it is about those guys," Hefner said. "They're a good team, obviously. They're a veteran team. I know how to get them out. I just didn't execute."
Hefner, who entered the game with an 11.02 ERA against Philadelphia in his career, was hit hard by the Phillies once again. He gave up eight runs on 10 hits over two-plus innings and came out of the game after allowing four straight hits before recording an out in the third. Hefner took his first loss since June 11.
While Matt Harvey and Zack Wheeler have drawn plenty of attention, Hefner had pitched brilliantly over the final month of the first half. He entered Friday's game with a 1.76 ERA since June 4.
But on Friday, Hefner missed his spots and lacked the extra velocity on his fastball that he's shown for much of this season.
"I think it was, a little bit, the break," Mets catcher John Buck said. "He was on such a good groove, too. He was a little erratic. I have complete faith he'll get back."
Philadelphia, though, was the one team he struggled against this season. He gave up five runs in three innings against the Phillies back in April, which had been his worst start of the year.
Hefner needed 38 pitches to get through a four-run, six-hit first inning, which included an RBI triple to center field off the bat of Chase Utley. Hefner retired the side in the second inning, but he fell apart in the third.
Mets manager Terry Collins said Hefner's problem simply came down to a lack of command.
"I don't think he hit a spot the entire first inning," Collins said. "Anything he wanted to throw, he didn't throw it there. He came in the dugout after he got the pitcher out and thought he might be settling in, and we get in the third inning -- he didn't throw a ball when he needed to."
Domonic Brown crushed a pitch into the upper deck in right field to lead off the inning. Hefner gave up three more hits, and Collins took him out of the game and brought in Greg Burke.
By the end of the third inning, the Phillies held an 11-0 lead, as Hefner's dominance before the All-Star break clearly didn't carry over to the second half.
Hefner said having so much time off during the break is no excuse for the way he pitched. He said he had a plan to prepare for Friday's start, and stuck to it.
But Hefner's velocity, which had been reaching 93 mph in his recent starts, was at 90 mph consistently on Friday. Collins said the sweltering 95-degree weather could've affected him. And although Hefner said the break wasn't an issue, Collins pointed to it as a possible factor.
"It could have been the seven days he's been off," Collins said. "I know he's pitched a lot better than he did tonight. We were as surprised as anybody about what happened. He's been throwing the ball so well."
Philadelphia starter Kyle Kendrick did enough to protect the Phillies' large lead, giving up six runs on nine hits over 5 2/3 innings.
"They hung in there with us. I think it was real hot," Phillies manager Charlie Manuel said. "At the end there, I think Kyle got tired and got kind of worn out. I think he was spent. The heat kind of got him."
Marlon Byrd hit a three-run home run in the fourth inning, and the Mets scored in each of the next two frames off Kendrick. David Wright added a two-run shot in the ninth, but there was no coming back in this one. The Phillies had already done all the damage.
Now the Mets have to hope Hefner reclaims the dominance he showed through those eight great starts.
"I needed to be a lot better than I was tonight -- especially coming out of the break -- and set a good tone," Hefner said. "I didn't do that."