We might know more about one of the Mets’ key second-half questions tonight, which is: Who is the real Mike Pelfrey?

At one time, Pelfrey was 9-1 and cruising toward the All-Star Game. All was right in his world and the Mets were making up ground on Atlanta. However, he has hit a rough five-game stretch since in which he’s gone 1-3 with a 7.52 ERA.

That’s just the beginning of the bad numbers.

In that span Pelfrey (10-4, 3.58 ERA) failed to make it out of the fifth inning in his last three starts, including going four while giving up four runs on 12 hits in his last start against the Braves.

Pelfrey admitted to a dead arm that might have led to a slight change in mechanics.

If anybody needed the All-Star break it is Pelfrey: “I think any kind of break is good. Whether it’s a day, three days, whatever. I think it’s always well needed.’’

His break got a little longer when Saturday’s start was pushed back until tonight because of a stiff neck.

But, it has been more than being tired that has hurt Pelfrey lately. His fall-off-the-table sinker has been up and flat, resulting in four homers in the five games.

When he was dominating early, Pelfrey kept his composure and was able to minimize the damage and shut down innings. Not anymore, and the deeper in trouble he gets the more he talks to himself like the troubled loner on the subway.

It looks as if he’s had a flashback to earlier in his career. However, it is premature to think he’s regressed instead of just hitting a wall that he now has to figure out a way to scale.

Pelfrey will attempt to get better tonight against Arizona, a team that has handled him well, especially in the desert, where he is 0-3 with a 7.16 ERA. Overall, Pelfrey is 0-4 with a 5.22 ERA in five starts against the Diamondbacks.

If Pelfrey is the pitcher he wants us to believe he is, he’ll have to find a way to stop the bleeding. He needs to figure this out. The season could depend on it.

John Delcos has covered Major League Baseball for over 20 years, including more than ten in New York on the Yankees and Mets beats. You can read more on his blog, New York Mets Report, where he hosts a chat room for each Mets game.