To begin what turned out to be the biggest week of his professional football life, Tim Tebow was down in the dumps.

All the Broncos were down.

By now, the country knows the Broncos would snap out of their doldrums in time to stun the heavily favored Pittsburgh Steelers 29-23 in overtime Sunday. Tebow’s exhilarating 80-yard dart-and-run pass play targeted Demaryius Thomas, who capped the game-winning touchdown on the first play in overtime by pulling a Bo Jackson and running straight into the tunnel that led to the victorious locker room.

“I was coming back out, and I got crushed,” Thomas said of his celebrating teammates. “Everybody got me in the tunnel.”

The sellout crowd of 75,970 at Sports Authority Field at Mile High erupted in celebration. Witnesses said that in Denver neighborhoods, delirious people were screaming from their balconies. Patrons at Denver-area bars were heard chanting, “Te-bow! Te-bow!”

BOX SCORE: Broncos 29, Steelers 23

Tebowmania is once again inflated. It was the Broncos’ first playoff victory in six years.

Heads up, Josh McDaniels. The new assistant coach of the New England Patriots was the Broncos’ head coach in 2010 when he drafted Thomas and Tebow in the first round.

Thomas, Tebow and the visiting Broncos will play New England at 6 p.m. Saturday in the second round of the AFC playoffs. The winner advances to the AFC championship game.

Thomas should be known as Mr. Big Catch. Just two years ago, the Broncos’ Brandon Marshall had 200 yards receiving while setting an NFL record with 21 catches. Thomas had 204 receiving yards in his first-ever playoff game on only four catches.

“This was the most accurate Tebow has been passing the ball,” Thomas said. “It was up to us as receivers to find the right spot.”

Tebow had just come off back-to-back rough performances against the lowly Buffalo Bills and Kansas City Chiefs to close out the regular season. He spent the week covering his ears from a deluge of insults from local and national media outlets.

Worse, Baltimore linebacker Terrell Suggs joined current players Steve Smith, Jermichael Finley and Joe Flacco in bashing Tebow, breaking the unwritten code already long broken by former players.

“I don’t get it,” said Champ Bailey, the Broncos’ star cornerback. “You can say it looks different or whatever you want, but don’t say he won’t make it. You don’t do that. This is like a big fraternity for me. Guys who do that, I lose respect for them.”

So what did Tebow do? He went John 3:16. That’s what Tebow thinks when he hears 316, anyway. Broncos fans of all beliefs will remember Tebow throwing for 316 yards and two touchdowns, and running for another score to outduel two-time Super Bowl winner Ben Roethlisberger.

The week’s happy ending had such a sorrowful beginning. The Broncos not only had lost the regular-season final to Kyle Orton and the Kansas City Chiefs last week, they fell by an embarrassing 7-3 score. All seemed doomed, playoffs or not. And the Broncos’ mood early last week reflected it.

“I think that’s fair to say,” Tebow said in a quiet hallway outside the home locker room. “We were down, but it was like a focus and very intense frustration that we wanted to get back on the field to show that wasn’t us. I feel like our attitude and mind-set kind of grew all week.”

Tebow said he awoke from his doldrums Wednesday, when the Broncos began their formal preparations for the Steelers.

During practice, a horn or whistle will blow marking the end of one period and the start of another. Tebow, the gung-ho Joe College guy that he is, sprinted from station to station. Everybody else walks or trots from one station to another. Tebow — after four preseason games, 16 regular-season games and 23 weeks of practice — sprinted from here to there. Between every period. At every practice.

“I wanted to be focused and have that game face all week,” Tebow said. “Not that I wasn’t enjoying it, but I wanted to have that focus and concentration all week.”

Helping Tebow last week was a push from team front-office boss John Elway, who advised his young quarterback to “pull the trigger.”

Tebow didn’t just pull the trigger, he started launching bombs. Early in the second quarter, he unleashed a beautiful 51-yard pass to Thomas. Two plays later, he threw a perfect 30-yard touchdown pass to Eddie Royal for a 7-6 lead.

“We tried to be aggressive,” Tebow said of Elway’s “pull the trigger” instruction. “I wanted to be aggressive and (offensive coordinator Mike) McCoy taught us to be aggressive, and guys really stepped up and made some great plays.”

The run-and-chuck offense was getting warmed up.

On his next possession, Tebow connected with Thomas again, this time for a 58-yard pass play to the Steelers’ 12. One play later, Tebow ran 8 yards on a quarterback draw off a four-receiver spread formation for a touchdown.

The Broncos were up 20-6 at halftime, but Roethlisberger, playing on a severely sprained left ankle, brought the Steelers back to a 23-23 tie with a 31-yard scoring pass to Jerricho Cotchery with 3:48 left.

“Yeah, I’ve watched him come through in Super Bowls,” Tebow said of Roethlisberger. “He’s such a clutch player. He was clutch today.”

Just as it appeared all was lost, Tebow delivered.

The Steelers called tails and the coin came up heads for overtime. On the Broncos’ first play, from the 20, Tebow winged a perfect pass to Thomas, who was crossing from left to right. Thomas stiff-armed away from one defender, Ike Taylor, and outran another who had the angle — and kept running until he left the stadium.

“He can still throw the ball better,” Broncos running back Willis McGahee said of Tebow. “It’s not like he can’t do it. He did it. But I know what they’re going to say next week.”

What’s that?

“Can he do it again?” McGahee said.

Mike Klis: 303-954-1294, mklis@denverpost.com or twitter.com/mikeklis

Bests

Wild way to win

Demaryius Thomas’ 80-yard touchdown on the first play of overtime Sunday replaced Champ Bailey’s 100-yard interception return six years ago as the biggest Broncos play in the history of Sports Authority Field at Mile High. Thomas’ touchdown beat the Steelers 29-23 and set off a wild celebration.

Play on in playoffs

The Broncos were 4-12 last season and started 1-4 this season. Now they’re in the AFC semifinals, against Tom Brady and the Patriots.

Tebow responds

After completing only 41 percent of his passes in a three-game losing streak, Tim Tebow threw for 316 yards and two touchdowns against the Steelers. He ran for 50 yards and one touchdown, wasn’t sacked and didn’t throw an interception. Lindsay H. Jones, The Denver Post

Worsts

Decker done

The Broncos’ victory Sunday came with a price. Wide receiver Eric Decker, left, is done for the season after taking a shot from Steelers linebacker James Harrison at the start of the second quarter. The Broncos will be short-handed at receiver against New England.

Defensive lapses

Denver’s defense was dented a lot in the second half, when the Broncos gave up big plays to Pittsburgh running back Isaac Redman and quarterback Ben Roethlisberger. The Steelers finished with 400 total yards. They had 170 at halftime.

Call it questionable

The Broncos were livid about their inability to challenge a third-quarter play ruled by officials as an incomplete Pittsburgh pass. Replays showed it was a lateral and forced fumble; the whistle sounded when the ball hit the grass. Lindsay H. Jones, The Denver Post

Pass/Fail

Offense

Tim Tebow certainly made the most of 10 completions with 316 yards and two touchdowns — 204 of those yards on passes to wide receiver Demaryius Thomas.

Defense

They opened up the playbook, playing a variety of looks that led to five sacks of Steelers QB Ben Roethlisberger to go with an interception.

Special teams

Matt Prater made three field goals, and the Broncos never lost their grip in a field-position game.

Coaching

Taking a page out of the Ravens’ script in Baltimore’s two wins vs. the Steelers this season, the Broncos often threw when the Steelers were in their run looks — and the Broncos are moving on because of it.

Game balls

QB Tim Tebow

A 316-yard performance to win his first playoff start is about all any player could want in that situation.

WR Demaryius Thomas

The 6-foot-3, 229-pounder was more than the Steelers’ secondary could handle with a staggering 51 yards per catch in the win.

S David Bruton

Made the right calls in the secondary and led the team with eight tackles.

Jeff Legwold, The Denver Post

Playoff OT rules

In the playoffs, the NFL rules change in overtime from the regular season.

In the regular season, it’s first team to score wins, unless a full quarter is played with no score. Then the game is a tie.

In the playoffs, each team is guaranteed a possession unless the receiving team scores a touchdown on its first possession, as the Broncos did. If the Broncos had kicked a field goal, Pittsburgh would have gotten one possession to try to tie the game or win it. In the playoffs, overtime is played in 15-minute periods until a winner is determined, and the game automatically ends upon any post-first-possession score (by safety, field goal, or touchdown) or when a score is awarded by the referee for a palpably unfair act. Source: NFL.com