Why Porcello’s jackpot contract made sense to Red Sox

No doubt Rick Porcello’s four-year, $82.5 million extension with the Red Sox was a stunner.

Porcello never has been an All-Star, never has pitched at the top of a rotation, and his career ERA, when adjusted to his league and ballpark, is below average.

So, how is it that Porcello is now set to earn nearly $120 million before age 31, the same age Jon Lester hit the open market with much lower career earnings?

Porcello, 26, is only three months older than Matt Harvey. The Red Sox will control him from his age 26 to 30 seasons (he is signed for $12.5 million this season; his new deal is from 2016 to ’19).

By contrast, James Shields signed a four-year, $75 million free-agent contract last offseason covering his age 33 to 36 seasons.

Porcello easily could have commanded a six- or seven-year deal in free agency, given that he would have been the youngest starter on the market — indeed, one of the youngest ever to hit the market.

That comes at a price. Porcello was only seven months away from free agency, and teams generally will pay a premium to prevent the players they want from gaining the right to negotiate with 29 other clubs.

AROUND THE HORN

Most teams use their own internal metrics, and the Sox recognize that they value Porcello more than some other clubs do, according to sources familiar with their thinking.

Porcello, when you include his $12.5 million salary this season, essentially will get $95 million over five years.

That’s approximately the same money the Cardinals gave Adam Wainwright two years ago to cover his age 32 through 36 seasons. Porcello is not nearly in Wainwright’s class, but he’s younger, healthier and the beneficiary of inflation in the market.

Reds right-hander Homer Bailey, who is represented by the same agency as Porcello, Excel Sports, cut a six-year, $105 million extension a year ago that covers his age 28 to 33 seasons. Porcello, a sinker-baller, lacks Bailey’s stuff, but Bailey signed at a more advanced age with more of an injury history.