There can be a fine line between mediocre and awful, and there’s little doubt who controls that line here in Mets camp.

We know that the Mets’ outfield will be abominable, and their starting rotation, infield and catcher all should be presentable, if far from excellent. Which leaves the bullpen as this team’s misery index.

“You look at last year, in the first half, we won some of these games, but we had 19 blown saves in the first half and still, we were eight games over .500,” Terry Collins said yesterday, after the Mets’ 4-1 victory over the Marlins at Tradition Field. “We win the majority of those games, all of a sudden we’re 13 games over .500. It’s a whole different look.”

The Mets actually stood at six games over .500 at the All-Star break, and they blew 13 saves in the first half; they blew 19 for the entire season. The Post excuses Collins for his imperfect memory. Wouldn’t you try to lose track of this stuff if you were the Mets’ manager?

His greater point stands, though. Just as we’re not talking about the Mets trying to win the 2013 World Series, we’re not suggesting they could have the world’s best bullpen. Just a competent one, which could lead to, conceivably, a season-long flirtation with .500.

In 2012, Mets relievers saved 65 percent of their opportunities, tying them with the White Sox for eighth-worst in baseball. They haven’t been better than average in this department since 2007, when they converted 70 percent of their saves to rank 13th.