Sure, you have to score touchdowns to win games, and the Vikings only scored on three field goals in Sunday's 20-9 loss at New Orleans, but they might have had a good opportunity for a touchdown drive that would have put them ahead had it not been for a critical 15-yard penalty on cornerback Captain Munnerlyn.

The Vikings limited their mistakes in their 4-0 preseason, but their loss to the Patriots last week was largely due to committing too many turnovers. Against the Saints, they didn't have any turnovers and were called for only five penalties, but the one against Munnerlyn turned the game around.

It came on the final play of the third quarter with the Saints up 13-9, when Munnerlyn slammed quarterback Drew Brees down on a sack. The unnecessary roughness call gave New Orleans a first down on a third-and-13 from its own 32-yard line, and what would have been a 9-yard loss ended up as a 24-yard gain because the penalty was enforced from the line of scrimmage.

There's no question the flag was easier for the officials to throw after Brees reacted as though he had been assaulted. He shoved safety Robert Blanton, who had landed on top of Brees as four Vikings had taken part in the sack.

And there is no doubt that NFL officials protect great quarterbacks such as Brees, Tom Brady and Peyton Manning more than the not-so-big-name quarterbacks.

Until that point of the game, the Vikings were playing much better than they did last week, and it looked as if they had an outside chance to score a big upset.

Coach Mike Zimmer told reporters after the game that the penalty shifted the momentum from the Vikings to the Saints.

"It was a pivotal point in the game," Zimmer said. "We had just sacked him, and they were going to punt the ball and they were going to punt the ball backed up. But it's a penalty, and you can't do those things."

The Vikings had trimmed their deficit to four after Teddy Bridgewater replaced injured starting quarterback Matt Cassel, who fractured multiple bones in his foot. They had held the Saints scoreless in the third quarter after giving up two touchdowns in the first half.

But after the penalty, the Saints marched down the field in seven plays, with Brees connecting with Marques Colston on an 18-yard pass for a game-breaking touchdown.

Zimmer was asked after the game what he saw on the Munnerlyn play.

"I talked to [referee] Walt [Anderson] about it afterwards, and he thought he threw him down with force," Zimmer said. "I asked if he blew the whistle when he was in the grasp, and he said, 'Yes.' Those guys are experts at what they do, so I'm not going to worry about that."

Zimmer was diplomatic about the play, saying that while the team will watch the film and see if they want to appeal the penalty, he added, "You can't throw the quarterback down."

The Vikings still had the fourth quarter to try to mount a comeback, so Zimmer hesitated to say that the penalty decided the game.

"I thought we had good momentum going on [at the time]," he said. "We were frustrating them a little bit offensively. We would have had good field position. Who knows? They were better than we were today."

Opportunity for rookie

Cassel's injury came early in the second quarter after he had thrown only 10 passes and completed five for 53 yards. It robbed the Vikings of an experienced quarterback with a better chance to win than with rookie Teddy Bridgewater. The first-round pick did some good things, though, posting a 83.3 quarterback rating as he completed 12 of 20 passes for 150 yards and rushed six times for 27 yards.

Cassel might miss the rest of the season. It's unfortunate for him, but for Bridgewater it's an opportunity to take all the snaps with the first team this week. The chance to play consistently will make him a much better quarterback.

"He is the quarterback," Zimmer said. "He'll be ready. I think it will help to go back home, it will help to get all the reps next week. I think that will be good for him."

With Bridgewater's inexperience, Zimmer said the staff simplified the playbook when he came in.

"If a situation like this arises, we have plays that obviously we feel better with him about, but yeah, we did taper it down some," Zimmer said. "He has not gotten all the reps during the week."

Now it is a good thing that the Vikings didn't trade Christian Ponder, who will dress as the No. 2 quarterback as long as Cassel is sidelined. Now the former starter will get some snaps to show offensive coordinator Norv Turner what he can do.

Bridgewater confident

With Cassel on the shelf and Adrian Peterson inactive, not to mention injuries to several other key players, this could very quickly become a rebuilding year for the Vikings, who are 1-2 overall.

It will be difficult for a rookie like Bridgewater to make his starting debut against the Falcons, one of the hotter teams in the league. One thing going in his favor is next week's game is at home. But after that game, Bridgewater and the Vikings will have a short time to prepare before facing the Packers in Green Bay in a Thursday night game.

Bridgewater, who is a very confident athlete, said in his news conference after the game that he is ready to be the starter.

"I'm going to be able to just get more practice reps throughout the week," he said. "As a backup it's all about having mental reps throughout the week. But for me, we have seven days to prepare for Atlanta and I have an opportunity to get those physical reps out there, develop that chemistry with the guys, and be able to be a better quarterback."

Bridgewater said he thought he had a good first performance, but with a lot of room to improve. He added getting in helped him understand the speed of an NFL regular-season game.

"The game is much faster," said the former Louisville standout. "You know it's the regular season now and guys are competing. You only get 16 opportunities and now we have 13 left. So guys are out there competing and playing at a high level. The competition was much faster and guys were more well-assigned."

Was Bridgewater nervous at all making his pro debut?

"Not at all," he said. "I wasn't nervous, because this is where I always wanted to be, and unfortunately the way it happened wasn't the way I expected it to. But I was able to go out there, I was relaxed, and the guys put the trust in me and they told me: 'Hey, nothing changes. The gameplan isn't going to change. You're going to continue to just play football."

Sid Hartman can be heard weekdays on 830-AM at 7:40, 8:40 and 9:20 a.m. and on Sundays at 9:30 a.m. shartman@startribune.com