Broncos head coach Josh McDaniels with his quarterbacks, from left, Kyle Orton, Chris Simms and Tom Brandstater, during Sunday's Denver-Dallas game.

Mark Reis / Colorado Springs Gazette / MCT

Josh McDaniels has gone from being Homer Simpson to being Ward Cleaver.

A month ago, the Denver Broncos were one seriously dysfunctional family. Disgruntled quarterback Jay Cutler had been traded to Chicago. In return, the Broncos got the quarterback the Bears didn’t want, Kyle Orton. Wide receiver Brandon Marshall, who’d caught 206 passes over the previous two seasons, also wanted to be traded. Unhappy because the Broncos wouldn’t rework the contract he’d signed as a fourth-round draft choice out of Central Florida in 2006, Marshall was pouting and petulant in practice –– moping, misbehaving and finally incurring a one-week suspension just prior to the season opener.

Amidst that maelstrom, there were doubts in Denver whether the 33-year-old McDaniels, who was 19 years old when his predecessor, Mike Shanahan, began coaching the Broncos, was the man for the job.

Flash forward to Sunday, when, the the Broncos and the Cowboys tied, 10-10, in Denver and only a little more than a minute left in the game, Marshall made a highlight-film catch-and-run –– leaping over a defensive back to haul in the ball, then eluding at least four other would-be tacklers on his way to a game-winning, 51-yard touchdown.

Afterward, when McDaniels was at his postgame press conference, Marshall bounded toward the wunderkind coach and, wonder of wonders, considering the way things were a month ago, embraced him in an affectionate bear hug while smiling from ear-to-ear.

It has turned around that quickly in Denver.

A season that began with internal bickering and widespread pessimism about the Broncos’ prospects has become a lovefest.

With that thrilling, 17-10, victory over Dallas, the Broncos are 4-0 heading into this Sunday’s major matchup with the Patriots, coached by McDaniels’ mentor, Bill Belichick.

Happy days are here again in Denver, where, even though the Rockies are in the playoffs for the second time in three years, after having won the National League pennant in 2007, when they were swept by the Red Sox in the World Series, the Broncos tower over the sports scene the way the Rocky Mountains do over Colorado’s capitol city.

Denver is the “Mile High City,” but football fans are riding even higher with their beloved Broncos unexpectedly undefeated.

Belichick, however, says he’s not surprised at the strong early results McDaniels has had after a rocky start to his tenure in Denver.

“It certainly doesn’t surprise me,” he said. “I have all the respect in the world for Josh – as a coach, personnel evaluator, and in general for his football knowledge and his ability to manage the game, whether it is as a coordinator or as a head coach.”

McDaniels was the Patriots’ offensive coordinator the past three years, after having been quarterbacks coach for two seasons before that. Although the Pats set scoring records while going 16-0 in 2007, when Tom Brady threw for a league-record 50 touchdowns – 23 of them to Randy Moss, also a league record – what is arguably equally impressive is that, when Brady was lost for the season in the first quarter of the first game last season, Matt Cassel came off the bench after not having started a game since he was in high school and led New England to an 11-5 record.

That prompted the Broncos –– who lost their last three games last season, finishing 8-8 and out of the playoffs –– to replace the accomplished Shanahan with the unproven McDaniels.

Shanahan had been in Denver for 14 years, winning back-to-back Super Bowls in 1997 and ’98. But, since then, the Broncos have won only one postseason game. Ironically, it was against the Patriots, in 2005. Over the last three years, Denver has been a mediocre 24-24.

In the final game of last season, the Broncos were routed by the Chargers, 52-21.

Through the first four games of this season, Denver has allowed a total of just 26 points – exactly half the total scored by San Diego in Shanahan’s swan song.

“They’re playing good football,” Belichick said of McDaniels’ Broncos. “They don’t beat themselves. They do a lot of things well, and that’s reflected in their record.”

As good as the Denver defense has been, it is on the offensive side of the ball that McDaniels has made his reputation.

“Josh is very creative,” Belichick said. “He’s got a great offensive mind.”

If he could come up with ways to put points on the board in New England with Cassel at quarterback, it probably shouldn’t come as a surprise he has done well in Denver, even without Cutler, traded to Chicago after going to the Pro Bowl last year.

Where only a month ago, there was doom and gloom in Denver, there now is sweetness and light.

Dreary, despondent, dysfunctional Denver has become a delighted Denver as McDaniels has gone from being like Peter Griffin in “Family Guy” to being like Howard Cunningham in “Happy Days.”

Except the youthful McDaniels looks more like Richie Cunningham. He not only looks young enough to be one of the players, he looks young enough to be one of the ball boys.

Look at this way – when Junior Seau was starring at Southern Cal in 1989, McDaniels hadn’t even started high school.

Now he’s preparing for his first game against his old boss, and there aren’t many in Denver – or in the Patriots’ coaching offices in Foxboro, for that matter – who doubt he’s up to the challenge.

jdonalds@projo.com