Tim Tebow is still giving the NFL whiplash.

Over the course of the regular season, he went from bad to good to occasionally spectacular, then back to being a bust. Such a bust, that all but one of the defensive coordinators preparing for the playoffs had already moved their game plans on the Broncos’ quirky QB from an email folder marked “active” to the “curiosities” file.

They hardly expected to see him again.

All those self-appointed experts who said Tebow couldn’t keep winning in the pros playing quarterback as if he were still in college were girding for the last laugh. That was supposed to come Sunday, when the Pittsburgh Steelers arrived with a banged-up, but still-No.1-rated defense in tow.

Instead, it’s New England’s turn.

“And I’m sure,” Patriots quarterback Tom Brady said, “there’s not a lot of guys on our team that slept great last night.”

Small wonder. The book on Tebow was supposed to be closed after he and the Broncos, winners of six straight at one point, lost their last three and looked clueless in the last two of those. Patriots coach Bill Belichick pulled it out when New England trounced the Broncos a month ago and it read something like this: Stack up defenders close to the line of scrimmage to stop the run; have a linebacker shadow Tebow, then move the corners and safeties around at the last second to disguise the thin pass coverage; dare him to throw the ball.

Denver coach John Fox faced similar schemes more times than he cares to count, but for the first quarter against the Steelers, the Broncos failed to complete even one pass. Pittsburgh safeties Troy Polamalu and Ryan Mundy kept creeping close to the line with almost every snap, leaving wide-open spaces behind them. The novelty of the “read-option” offense the Broncos adapted from the college game for Tebow’s sake appeared to have the shelf life of a carton of raspberries. Then the second quarter rolled in and Tebow looked like Steve Young, completing four passes of 30 yards or better, something that hasn’t been done in the NFL in 50 years.

A day later, Fox struggled again to explain the transformation.

“You know, football is football,” he said.

But the fact that his offense worked so well at some times and so poorly at others still seemed a mystery. Fox finds himself defending the scheme as often as opponents do.

“They played that kind of football at a pretty high level in college, you know, and there have been some very successful, productive offenses in this type of offense. But it’s a little unique for the National Football League,” he conceded.

That’s because once the novelty of the “read-option” wears off, once the league’s defensive brain trusts have enough game film to study it, they should be able to shut down the run component. Also, Tebow has yet to prove he can win a game playing like a conventional NFL passer. There’s also the danger of exposing a running quarterback to frequent collisions with NFL-caliber safeties, who run like deer and deliver hits like compact SUVs. That last thought may have crossed Fox’s mind.

On paper, it looks like a mismatch: Tebow against Belichick, who’s been successfully scheming how to ruin a quarterback’s life long before Tebow was born. Then again, the same could have been said about Dick LeBeau, who called the shots for Pittsburgh’s defense and learned a new trick to his everlasting regret on the first play of Sunday’s overtime period.

No one expected Tebow to make it out of there.

No wonder he smiled mischievously when he said afterward, “We keep believing.”

Even if few others do.