SANTA CLARA – As 49ers players filed out of team headquarters Monday morning, one word was repeated: bittersweet.

The 49ers enter 2009 puffed up after winning four of their last five games. Still, there was regret that the music ended prematurely on the 2008 campaign.

Several players cited one game in particular, the team's 29-24 loss in Arizona on national television Nov. 10, in which miscommunication on the game's final play left the 49ers a yard and a half short of a game-winning touchdown and perhaps a trip to the postseason.

"If we could've closed that game in Arizona, we wouldn't be having this conversation right now," said linebacker Takeo Spikes. "We'd be talking about the playoffs."

The game was the second under then-interim coach Mike Singletary.

In his first, a lopsided 34-13 loss to Seattle, the 49ers played as flat as they had all season. Singletary was famously furious at halftime, and before the end of the game banished one of his marquee players, tight end Vernon Davis, to the locker room.

"It's one of those things where it's coach Singletary making a statement and saying, 'Look, I'm going to hold you accountable. You better hold yourself accountable. Let's hold each other accountable,' " quarterback Shaun Hill said. "I think a lot of people took notice of that."

The bye week between the Seattle and Arizona games gave Singletary two weeks to put his stamp on his team. And although they fell short in the Arizona desert, the 49ers showed a fire in that game that would be their calling card for the rest of the season.

Singletary has never been a defensive coordinator, and indeed his lack of an X's and O's background created the perception that his success was built entirely on emotion.

Some of the tactical decisions he made upon getting the interim job suggest otherwise.

The first was overruling offensive coordinator Mike Martz by replacing J.T. O'Sullivan with Hill at quarterback. Hill finished third in Martz's quarterback competition last offseason, but his safer style of play translated into wins for the 49ers.

With Hill under center, Martz didn't ask for as many seven-step drops. That reduced the number of big pass plays, but also cut down on the sacks and turnovers that plagued the 49ers under O'Sullivan.

Though Hill played one more game than O'Sullivan, he was sacked nine fewer times and threw three fewer interceptions. Hill lost two fumbles while O'Sullivan lost six. He also topped O'Sullivan in touchdown passes – 13 to eight.

Singletary also simplified the defense.

Under Mike Nolan, the unit had vacillated among a 3-4, 4-3 and nickel scheme depending on the opponent. Singletary mostly stuck to a 3-4 alignment, which allowed the 49ers' two best pass rushers – linebacker Parys Haralson and defensive lineman Justin Smith – to be on the field at the same time. Haralson led the team with eight sacks; Smith had seven.

Mostly, Singletary got his players to believe in – and care for – each other.

He began arranging for meals at the end of the day to encourage mingling among the team. He did away with Nolan's "Win Monday" – a day off for players – so that players could bask in the glow of a win together.

When Hill struggled two weeks ago in St. Louis, he not only received encouragement from his fellow offensive players – defensive players on the sideline showed their support, too.

Davis, who became one of Singletary's biggest advocates as the season drew to a close, said that Singletary inherited a team with three distinct units: offense, defense and special teams.

Today the 49ers are one.

Said Davis: "And that's something we never had here."

Read Matthew Barrows' 49ers blog at www.sacbee.com/ninersblog.