Bill Belichick put an extra receiver on the field to confuse the Baltimore Ravens.

Now the New England Patriots coach will find out how it feels.

Defending against Colts quarterback Andrew Luck is “like a sixth receiver you have to cover,” Belichick said on Tuesday, an ironic choice of words in the wake of his innovative use of an ineligible receiver in the 35-31 victory over the Ravens.

“If (Luck) extends the play, then he has the ability to create big plays. We’ve seen him do that multiple times throughout his career already,” Belichick said. “It’s another guy you have to defend in the running game, the passing game in terms of his ability to scramble and make first-down yardage on possession-type downs. And he makes good decisions, so all those things are a problem.”

The Patriots advanced to their fourth consecutive conference title game on Saturday thanks in part to a series of plays in which they only sent four traditional offensive linemen onto the field. A skill player then declared himself ineligible — but too late for the Ravens to get the matchup they wanted.

Baltimore coach John Harbaugh said he just wanted the referee to give him time to make a substitution. But by the time he got that straightened out the Patriots had marched down the field.

Now New England is facing a player who redefines his position.

And it’s not going to be easy, Belichick conceded.

“Look, he’s passed for a lot of yards in a lot of games,” the Patriots’ coach said. “The guy is a really good quarterback. He can do everything that a top quarterback needs to do,” listing all of the things Luck can do with his arm, his legs and his mind.

“He’s got good poise, good vision, handles the team well. He’s a smart player in terms of game management and situational football,” Belichick said. “So I’d say all of those things are strengths. They’re all assets. He does a good job of all of it. There are a lot of things about his game that are very good and hard to defend.”

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