IRVING, Texas — Boosted by a 4-0 December to Remember, the Dallas Cowboys head into the postseason believing they will go all the way to the Super Bowl.

It all starts Sunday as the 12-4 Cowboys welcome the 11-5 Detroit Lions for what might be a very wild, wild card game.

The Cowboys’ mood is far different after they finally rose above three straight 8-8 seasons to the NFC East title and a trip to the playoffs for the first time since 2009.

“It feels really great,” tight end Jason Witten said. “I think for a core group of us that took it under the chin the last three years, we knew we had to go do it. We put our head down and had a chip on our shoulder. We had to play better. We had to practice harder. We had to be smarter, tougher and more physical. It’s good to see it pay off, but it’s just getting started.”

The Cowboys open the playoffs pitting strength against strength — the Dallas offensive line against the Detroit defensive line, which features controversial tackle Ndamukong Suh, who is playing in this game only after his suspension was reduced to a fine.

His presence is seen as a key factor against a Cowboys offense that features the NFL’s leading rusher in DeMarco Murray, who led the league in rushing with 1,825 yards.

If Suh were forced to sit out this game, history might have recalled his absence as a factor if the Cowboys won, especially if they had an effective running game.

Regardless, the Cowboys had no reaction upon hearing Suh’s suspension was lifted and he could play in Sunday’s wild card game.

“No real reaction,” Dallas coach Jason Garrett said. “Again, we’re focused on ourselves. Obviously, he is a good football player, they have a good defensive team and he is a big part of it.”

Quarterback Tony Romo said, “We just go play. Our mindset all year has been whatever time, whatever day, whoever we’re playing against … It just doesn’t change for us. We’re going to go out and play. I think that’s worked well for us just to go put our head down and attack whoever we’re going against and not worry about what’s going on around you.”

In Dallas’s 4-0 December to Remember, Romo was named NFC Offensive Player of the month. The 34-year old quarterback completed 74.8 percent of his passes for 987 yards with 12 touchdowns and one interception in leading the Cowboys through that 4-0 December.

“Yeah, he’s played very well,” Garrett said. “We don’t get caught up in Player of the Week, Player of the Month, all of that stuff, but he’s certainly played very well. There’s no question about that.”

So the Cowboys think they can go a long way in the playoffs because they finished the regular season as hot as any team in the league.

The Cowboys won four straight games — against the Chicago Bears (41-28), Philadelphia Eagles (38-27), Indianapolis Colts (42-7) and Washington Redskins (44-17).

“It’s been a pretty good December, but we’re going to keep it rolling into the playoffs,” guard Ron Leary said. “It’s going to get better.”

The Cowboys believe they can finish because they have been in playoff mode for the last month. But most important, it’s because they are team with a different attitude, a fighter’s spirit that was instilled in them since the off-season.

They proved in 2014 that they are no longer the team that wilts in the fourth quarter, blowing late leads and playing its worst football when it matters most. There were fighters this year, going 4-0 in December for the first time since 1993 and 5-1 in games that were within a touchdown in the fourth quarter.

“What you try to emphasize, as a coaching staff to your football team, is the importance of finishing everything,” Garrett said. “You’re always trying to instill that. You certainly try to put players in situations where they have to finish plays, finish a certain situation in practice. So it’s a word that we probably use as much as any, and certainly finishing games and finishing the season follow those kinds of things.

“The best teams I’ve been around were great finishers: the runners finished, the linemen finished, the great tacklers. That’s what this game is all about. You’ve got to finish the job. Again, that’s a mentality, that’s a mindset. You’ve got to after it. And you’ve got to go finish the job the right way. I think championship teams, by definition, finish well.”

THE SERIES: 26th meeting. Dallas leads the series 13-12. They are tied 1-1 in the playoffs. Dallas has won five of the last eight in the series, but Detroit has won the last two, including 31-30 in 2013. The Cowboys are 8-3 against the Lions at home. They are 1-0 against the Lions in the playoffs at home.

NOTES: LB Rolando McClain (flu) was limited in practice on Wednesday. He remains slowed by the illness but should play in the game. … LB Anthony Hitchens missed practice with a high ankle sprain. … RT Doug Free, who missed the last two games with a sprained ankle, sat out practice again Wednesday but might be ready for game. … S C.J. Spillman (groin) did not practice on Wednesday because of a groin injury.