Harrison Smith cut in front of a receiver, snagged his first career interception, weaved into the end zone, withstood a beating from his teammates and finally made it back to the bench, where he donned an oxygen mask.

Maybe he was winded. Maybe he was just trying to hide a grin. After all, it's hard to have a better weekend than Smith did without hearing the phrase ''lump sum.''

Saturday, Smith watched his alma mater, Notre Dame, remain undefeated. Sunday, he made the key play in the Vikings' 21-14 victory over Arizona, making them 5-2 and one of the most surprising teams in the NFL.

''Usually, I try not to get too excited,'' he said. ''I get tired if I get too excited. But it's hard not to get excited when you score.''

When you sign up to play safety for the Vikings, they don't provide a guide to end-zone celebrations. Usually, when Vikings safeties wear a mask, it's to hide their identity.

Smith's interception was the first by a Vikings safety since 2007. His touchdown was the first by a Vikings' rookie defender since 2003. Since Darren Sharper left the franchise, Vikings safeties have served mostly as extras in other teams' touchdown videos.

''I love him,'' said cornerback Antoine Winfield. "The guy comes to work every day. He's very smart. You can tell he's a real football player. Great knowledge, great football awareness, and he's making plays on the field, which is rare for a young guy. We haven't had that consistent playmaker in the secondary since Sharper."

Sharper's intelligence and hands allowed him to prey on hesitant quarterbacks. Smith seemed to be channeling Sharper when the Cardinals faced third-and-6 early in the third quarter.

The Vikings led 14-7, but didn't score another offensive touchdown. John Skelton dropped back and, under pressure, was looking for receiver Early Doucet, who was covered by Winfield. Smith read Skelton's eyes and stepped in front of Doucet, then weaved to the end zone.

"I played high school in offense, so I scored then,'' he said. "It's been awhile since I've gotten into the end zone, though. We got pressure on him, so he stepped up, and I was looking where he was at. It was a play where I had the freedom to go after it.''

At a glance, the Vikings' 5-2 record seems mysterious. It is less so when you consider their schedule (they've played only one team that seems sure to make the playoffs) and the quality of their draft.

General Manager Rick Spielman was able to make two draft-day trades that enabled him to land left tackle Matt Kalil and Smith in the first round. Add kicker Blair Walsh, who turned out to be a steal in the sixth round, and promising cornerback Josh Robinson, taken in the third, and Spielman was able to immediately bolster his offense, defense and special teams.

"Rick and the personnel department did a great job of presenting who the top safeties were in the draft and where they might fall for us,'' Vikings coach Leslie Frazier said. "The good news for us was we had been around Harrison at the Senior Bowl, so we had some inside information on how he would fit in our defense and our scheme, with the intel we got from Rick and his scouts about Harrison.

"He was a guy that we targeted. We didn't know if we were going to be able to get him.''

The Vikings are demonstrating the exponential effect of good players. Adrian Peterson and Percy Harvin have enabled a limited offense to move the ball. Kalil has helped transform the offensive line from a weakness into a strength. Walsh has all but eliminated kickoff returns and won games with his field-goal range.

Smith has proved stout enough to help on third-and-1 and savvy enough to help on third-and-20.

"It's a breath of fresh air, some of the things he has done and has been able to do throughout the season,'' Frazier said. "The tackles, the presence we have with him, and to be able to find a way to get that ball into the end zone.''

Jim Souhan can be heard Sundays from 10 a.m. to noon and weekdays at 2 p.m. on 1500-AM. His Twitter name is SouhanStrib. • jsouhan@startribune.com