FOXBOROUGH, Mass. — The New England Patriots defense has five rookie starters. Their top two rushers weren’t drafted. Their strength of schedule is the sixth toughest in the NFL.

And their record is the league’s best.

The transition from an old team that won three Super Bowls to a successful young group has been a speedy one. Of their 53 players, 23 are in their first or second seasons. Youngsters have made major contributions to the Patriots 6-1 record.

“That’s just a testament that we’re all buying into the system,” cornerback Kyle Arrington, in his first year as a starter, said Monday. “We read the sign (near the locker room) when we leave and we read the sign there when we come in. And it says, ‘Do your job.’ And if you don’t do that, we can’t be successful.”

That job isn’t easy, not with Coach Bill Belichick’s complex game plans. Those who can’t comprehend or work hard don’t last long. Those who can do that stick around, no matter their draft position, reputation or contract size.

Or age.

“We’ve got a lot of young players, but I don’t really care about all that,” Belichick said. “What I care about is how the team functions as a unit.”

It’s functioned very well under Belichick, now in his 11th season as the Patriots coach.

They won the AFC East in six of the past seven years. They reached the playoffs in seven of the past 10. Through seven games from 2003 through 2010, they were 7-0 once, 6-1 and 5-2 three times each and 4-3 once.

But Richard Seymour, Rodney Harrison, Tedy Bruschi, Mike Vrabel, Asante Samuel, Randy Moss and Laurence Maroney were on many of those teams. All are gone now.

Now the Patriots, who had a checkered drafting record for much of the decade, have nine players from the 2009 draft and eight from 2010 — including rookie defensive starters Devin McCourty, Patrick Chung, Jermaine Cunningham, Brandon Spikes and Brandon Deaderick. Aaron Hernandez, a fourth-round pick this year, has the third most yards per catch, 13.4, among NFL tight ends.

“I think it is really hard with young players to project and predict how it will go,” Belichick said. “At some point, when you have enough experience and the results are in over a significant period of time, I think there is a point where you have a much better gauge on it. But sometimes that isn’t until two or three years down the road.”

The Patriots beat the Minnesota Vikings 28-18 on Sunday. The New York Jets and Pittsburgh Steelers, the only other teams that began the day with just one loss, both dropped their games.

New England’s next test comes Sunday at the Cleveland Browns (2-5). The two games after that should me much tougher, at Pittsburgh and at home against Indianapolis.

This season’s success has all but washed away last season’s finale, a surprising 33-14 loss to the Baltimore Ravens in the first round of the playoffs, a game New England trailed 24-0 after one quarter.

Of course, receiver Wes Welker wasn’t in that game, and his return this year has been a boost. He has 40 catches and has made an unexpectedly quick recovery from major knee surgery. At the same time, though, he hasn’t reached his pre-injury level.

“We’ve got a lot of heart,” guard Stephen Neal said. “Things are stacked up against us and we just keep plugging away.”

Tom Brady, further removed from season-ending knee surgery after the 2008 opener, is playing better than he did last year and is the NFL’s fifth-rated passer, with 12 touchdown passes and just four interceptions.

“We’re winning close games. We’re winning tough games and I think that’s what it takes,” he said.

“You’ve got to win on the road. You’ve got to beat good teams. You’ve got to win when you’re down.”

They’ve done all of that.

They’ve won all five games since a 28-14 loss to the New York Jets. They’ve won two of their last three games by three points and the other by 10. They led the Vikings 21-18 midway through the fourth quarter, then held the ball for 5 minutes, 30 seconds on a 13-play drive capped by BenJarvus Green-Ellis’ second touchdown of the game, a 2-yard run.

Green-Ellis had just 100 carries in his first two seasons after arriving as a free agent out of Mississippi. This season, he has 371 yards and six touchdowns on 85 carries, most of them since Maroney was traded to Denver after the first game.

The Patriots added 5-foot-7-inch running back Danny Woodhead that same week after he was released by the Jets, who originally signed him in 2008 as a free agent from Chadron State. He’s rushed for 178 yards and two touchdowns.

But there’s still plenty of improvement to be made.

“We’ve got to start much better and play better in the first half,” Welker said.

Arrington, a rookie free agent with Philadelphia in 2008, was primarily a special teams player. But when Darius Butler struggled early this season, Arrington became a starter and has played well alongside safety Patrick Chung, a 2009 second-round pick and cornerback McCourty, a 2010 first-rounder.

“I like how we’re just coming together as a team, growing more comfortable with each other on and off the field,” Arrington said.