Darrelle Revis was the missing piece. He was the difference between the Patriots having a contending team, and a Super Bowl-winning team.

It was the perfect marriage last year. Both sides got what they wanted.

Now Revis is a Jet.

So much for the “Drive for Five.” Now, it’s looking more like the “Drive to Survive.” Especially if the secondary also says goodbye to Brandon Browner, which is a possibility given the Patriots did not pick up his option yesterday, making him a free agent.

Bottom line?

Without Revis, the defense you saw last year just went poof! It doesn’t exist anymore. Having Revis and his ability to take away the opposing team’s top receiver on his own was a game-changer. He allowed Bill Belichick to do so many things with the unit.

This was not the cover-2 zone of previous years that surrendered tons of yards. This wasn’t the defense that couldn’t get off the field on third downs, or just couldn’t make the plays at key points.

This year, Belichick wasn’t afraid to send in safeties to blitz. He wasn’t afraid to send in linebackers to blitz. He wasn’t afraid to roll coverages. He wasn’t afraid to have Revis eliminate different players at different times.

During the Week 11 game against Detroit, Revis was asked to shut down Golden Tate, Calvin Johnson (on the goal line) and Eric Ebron during certain points in the game.

And he did just that.

Or, he could just erase one guy, whether it was Demaryius Thomas or Sammy Watkins.

Belichick doesn’t have anyone who can do that job. There’s no one in-house, and no one in free agency who fits the bill to the level of Revis’ ability. And with the Pats picking at No. 32, it’s doubtful of Belichick getting that kind of shutdown corner in the draft.

So maybe Belichick should turn his attention to the offense and load up there, because he’s going to have to score a lot of points when he goes back to that cover-2 zone.

And who replaces Revis?

Malcolm Butler made a huge name for himself during the Super Bowl with the game-winning interception, and certainly deserves more playing time. He’s a nice player, and plays aggressively and fearlessly, but he still has a long way to go.

The other corners are Logan Ryan, Alfonzo Dennard and Kyle Arrington. The latter is better suited as a slot corner. He doesn’t work as well playing on the outside. Butler overtook Dennard on the depth chart last year, and Ryan was largely inconsistent.

Of course, they can re-sign Browner, but as a big, tough physical mauler, he was the perfect fit opposite Revis. He’s a great No. 2. He’s really not a No. 1 cornerback. No one currently on the depth chart fits that profile.

That group, collectively with Revis and Browner, was special. As a secondary, with safeties Devin McCourty and Patrick Chung, it fit together like a glove.

But Belichick wasn’t willing to bend for Revis to keep it together. He doesn’t bend for mercenaries. That’s clearly not his style. When it comes to contracts, it’s usually his way or the highway.

That’s why Revis is with the Jets, agreeing last night to a five-year, $70 million deal with $39 million guaranteed, and leaving the Patriots in scramble mode.

Last year, the dynamics were different. Belichick and Revis needed each other. The Patriots lost top corner Aqib Talib to the Broncos in free agency, while Revis, released by Tampa Bay, wanted to re-establish himself as the best corner in the game on a contending team. It was the perfect marriage. That’s why the money, and the contract, wasn’t much of an issue.

A year later, Belichick still needs Revis to put his defense over the top, but the elements changed.

Revis won a Super Bowl, and put himself back in the conversation as the game’s best corner. The money mattered more than last year. Instead of the perfect marriage, it became the perfect storm.

So the Patriots are down a shutdown corner, and back in cover-2 mode. That’s not the place to be if you want to repeat as champions.