The Mets have lost four of their last five games. The losing pitcher in each one has been a reliever.

Welcome to Reality Check 101: If the Mets are going to hold off the Nationals and win the NL East, they are going to have to be able to depend on their bullpen. It's a unit that has overachieved for most of the season, but has shown serious signs of fraying in the last week.

In the last five games, Mets relievers have allowed 15 runs (13 earned) in 181/3 innings against the Pirates and Orioles. Bobby Parnell suffered two of the defeats and then was told by the team to go on the disabled list with what was termed right shoulder tendinitis.

Sean Gilmartin and Carlos Torres were the other losing pitchers. On Wednesday in Baltimore, Torres allowed a walk-off home run to rookie Henry Urrutia in the ninth inning of a Mets 5-4 defeat.

Two innings earlier, Hansel Robles gave up a game-tying homer to Adam Jones.

"When you don't make pitches, when you don't locate, you're going to get hit," manager Terry Collins said. "It's pretty simple. That's what's pitching is about. You've just got to make the pitches you're supposed to."

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Collins believes he can depend on Tyler Clippard and Jeurys Familia, although the closer walked in two runs in the ninth inning of Tuesday's 5-3 victory before notching his 33rd save.

Collins chose not to use Clippard for more than an inning on Wednesday and didn't bring Familia into a tied game on the road. Both had pitched on Tuesday, but the Mets had off days on Monday and Thursday.

Collins has made it clear he's not going to overuse Clippard and Familia. So with Jenrry Mejia suspended for steroid use and Parnell on a timeout, what are the Mets' options to bolster the back end of the bullpen?

Make a trade: Players can still sneak through waivers and get traded, as you saw with Chase Utley going to the Dodgers on Wednesday and former Met Marlon Byrd getting dealt to San Francisco on Thursday. But Mets officials are not optimistic they'll be able to pull off another significant deal before the Aug. 31 postseason roster deadline.

Young guns: The Mets could give expanded roles to Logan Verrett, Erik Goeddel or even Vic Black. But there are issue with all three.

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Verrett may make a spot start in place of Matt Harvey on Sunday in Colorado. The Mets want to skip Harvey to keep him under his innings limit. That's why Collins removed Verrett from Wednesday's game after he had recorded three outs on six pitches. The next pitcher in was Robles.

Goeddel, who had a 1.96 ERA in 22 games earlier in the season, is rehabbing an elbow strain with Double-A Binghamton.

"I'm healthy, Goeddel told the Binghamton Press & Sun-Bulletin. "I'm just trying to fine-tune things, kind of get back to where I was before the injury in terms of sharpness of all three of my pitches so when they do call me back up to New York I don't miss a beat."

Black, who was supposed to be an important piece, has struggled with injuries and ineffectiveness at Triple-A Las Vegas.

"Good arm," Collins said. "When he throws strikes, he does well. When he walks the leadoff hitter, he has some troubles."

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Steven Matz: The Long Island lefty, who made his second rehab start Thursday night for Class-A St. Lucie, could be a formidable weapon out of the pen. But the plan is for Matz to fill in for Harvey or Noah Syndergaard as a spot starter or be part of a six-man rotation after rosters expand on Sept. 1.