Closer Jenrry Mejia throws a pitch in the ninth inning...

Closer Jenrry Mejia throws a pitch in the ninth inning during a game against the Philadelphia Phillies at Citizens Bank Park on August 10, 2014. Credit: Getty Images / Hunter Martin

Terry Collins has often relayed a tidbit of advice he heard at the beginning of his coaching career.

Young players, he was told years ago, can leave a manager vulnerable. They lack the reliability of veterans and make mistakes, many of which can be costly. And like players of all ages, they get hurt.

In one torturous afternoon Sunday for the Mets, all of those harsh lessons came to life.

It began when Rookie of the Year candidate Jacob deGrom was sent to New York for tests on his sore right shoulder. It ended when Jenrry Mejia revealed that he has spent the last three weeks pitching through a sports hernia that likely will require surgery after the season.

Mejia's admission came moments after he blew the save in a 7-6 loss to the Phillies, who erased a five-run deficit.

"As we've discussed every day now for the last three weeks, we're walking this fine line, trying to make sure these young kids stay healthy," said Collins, whose team has gotten younger and more inexperienced as it has faded from contention.

Those efforts to protect their young players haven't shielded them from injury. And they were reminded of that reality before the game when deGrom, 26, was scratched from Tuesday's scheduled start.

"I'm calm about it," said deGrom, who felt soreness after his last start Thursday. "I don't think it's going to be serious. I could probably go out there and pitch with it right now. But just talking to them, at this time of the year, it's not really worth pushing it. If I can skip one and be 100 percent and let it calm down, that was kind of what they talked about."

DeGrom is 6-4 with a 2.87 ERA in 16 starts and has been the Mets' top starting pitcher this season. "I'm not overly concerned except he's a young kid who's got a sore shoulder," Collins said. "That scares me."

Mejia, 24, already has battled through myriad injuries, including bunions, a sore forearm after getting struck with a comebacker and tightness in his calf and back. Team doctors have cleared him to keep pitching with the hernia as long as he can deal with the discomfort. "Everything's OK,'' he said. "Tight. But it's OK. That's no excuse . . . I want to keep pitching."

Collins has obliged him, even though his performances lately have been nerve-wracking.

For a time, it appeared Mejia might get another day off, just as he did Saturday for what the team called lingering soreness in his right calf. (It turned out to be a concession to the hernia.)

The Mets built a 6-1 lead at one point, and Zack Wheeler allowed three runs in six innings, notching yet another quality start. Juan Lagares drilled a two-out, two-run triple in the third and Lucas Duda and Travis d'Arnaud homered on consecutive pitches in the fifth.

But Chase Utley bashed a two-out, two-run triple in the seventh, adding to his earlier solo homer. Suddenly, the Phillies had pulled to within 6-5.

In the ninth, Cody Asche lined a leadoff double down the rightfield line and Marlon Byrd lined an RBI single to tie it.

Three batters later, with the count full, Collins intentionally walked Utley to pitch to the slumping Ryan Howard, who pulled the winning hit just inside the line in right.

Mejia insisted he will keep pitching and Collins said he will let him, adding: "If he tells me it bothers him, then we'll need to make adjustments."