Less than two weeks ago, seemingly everybody outside the Mets clubhouse was wondering why struggling Frank Francisco was still their closer. Lately he's showing why. A change in his bullpen sessions has made a change in the Mets' maligned pen as Francisco has given them some much-needed endgame stability. He has retired a dozen straight since a sketchy outing in Toronto, including a perfect ninth inning in yesterday's 2-0 shutout of San Diego. And Francisco — whose 13 saves are one off the NL lead — told The Post it's due to a subtle change, throwing his bullpen sessions off the mound instead of flat ground.