As they move toward their first postseason berth since 2006, the Mets shored up one of their few weaknesses Saturday, agreeing to terms on a trade with the Diamondbacks for reliever Addison Reed.

A source confirmed the trade, which will not become official until after a medical review. It's unclear whom the Diamondbacks will get in return.

The Mets have been in search of a more reliable bridge leading up to setup man Tyler Clippard and closer Jeurys Familia.

In the 26-year-old Reed, the Mets found an arm who might fit the bill. The one-time closer is 2-2 with three saves and a 4.20 ERA in 38 appearances with the Diamondbacks.

But he has been much better since returning from a stint with Triple-A Reno in late July, posting a 1.65 ERA in 16 1/3 innings in 13 relief appearances.

Though Reed is arbitration- eligible and is under team control next season, the righthander appears destined to be a rental. He's making $4.9 million this season and would cost more than that to retain next year.

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Nevertheless, in the short term, he gives the Mets a much-needed alternative, especially against lefties. Although Reed is a righthander, lefthanded hitters have a .665 career OPS against him and righthanded hitters are at .755.

Reed cleared waivers this past week, making him eligible to be traded. He will be added to the roster before the Aug. 31 deadline for postseason eligibility.

In the short term, he almost immediately will help a Mets bullpen that has been so taxed that starter Bartolo Colon was pressed into relief work in Saturday's 3-1 loss to the Red Sox.

"I just think right now they're tired," manager Terry Collins said before the game. "They've got through a stretch . . . where we were getting five and six innings out of our starters. We've worn them out."

Colon tossed a scoreless ninth inning on what would have been his bullpen day. He's still expected to start Monday against the Phillies.

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Colon made his first relief appearance since 2011. Collins insisted that the outing was a matter of necessity, not an audition for a bullpen role in the playoffs.

The Mets have been aggressive in pursuing bullpen help after the non-waiver trade deadline, submitting waiver claims on multiple relievers, according to a source.

Though the Mets aren't close to any other deals, they will continue to monitor the market. Though they were awarded the claim for Padres reliever Marc Rzepczynski, a source said the Mets are unlikely to trade for the lefty.

Instead, the Mets could have a competition on their hands.

Rookie Hansel Robles (3.80 ERA) has earned consideration for a larger role, as has lefty Sean Gilmartin (2.25 ERA). Logan Verrett (1.93 ERA) also has made a push for a spot in the bullpen should the Mets make the postseason.

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Lefty Eric O'Flaherty has posted a 12.86 ERA, though he is coming off a pair of scoreless outings and could push for a specialist role.

Two expected September call-ups, righty Erik Goeddel and lefty Dario Alvarez, also could factor into the mix.