The goal every game is to hold opponents to 17 or fewer points. Defensive coordinator Tracy Claeys has preached that for years, and it is ingrained in the Gophers now that they are playing their best defense since the turn of the century.

The Gophers are tied for 15th in the nation in scoring defense at 18.7 points allowed per game, and that number is dropping.

Since a tough first half at Texas Christian, the Gophers have given up 44 points over their past 14 quarters, which equates to 12.6 points per game. This roll they are on defensively is a big reason they're nearly two-touchdown favorites against Purdue on Saturday, with a similar line expected next week at Illinois.

Claeys wasn't thrilled with every defensive play in Saturday's 24-17 victory over Northwestern. The Wildcats mounted two long touchdown drives, racked up 269 passing yards, and converted on 45 percent of their plays on third and fourth down.

"I tell the kids all the time, 'Offenses practice, too,' " Claeys said. "The good thing about it is, at one time here [with the Gophers], 17 points — I probably could have run for mayor. Now, everybody is frustrated."

Claeys finished that thought with a big smile.

In 2010, the Gophers' final year under Tim Brewster, they allowed 33 points per game. When Jerry Kill arrived with Claeys that December, they made defense the top priority. The unit has improved steadily ever since. Though it's only a half-season, this is the best the defense has performed since the Gophers gave up 16.3 points per game under Glen Mason, in 1999.

"I think we're playing with very good discipline right now," Kill said. "We're not having very many mental errors at all. Being unselfish, just doing their job. And we've very athletic. Our linebackers are long, and I think length and speed certainly helps you."

The Gophers were good defensively last year, allowing 22.2 points per game, but they had to replace five senior starters, including NFL draft picks Ra'Shede Hageman and Brock Vereen. They lost a potential starting linebacker, Cody Poock, to a torn anterior cruciate ligament during spring practice. And starting defensive tackle Scott Ekpe tore an ACL on the first series of the season.

But others have filled the big-play void. Middle linebacker Damien Wilson leads the Big Ten with 11 tackles per game. Defensive tackle Cameron Botticelli was an unsung performer in previous years, filling holes that enabled others to make big plays. This year, he's doing both, as he leads the team with 5.5 tackles for a loss. Ekpe's replacement — true freshman Steven Richardson — isn't far behind on that list with four.

The Gophers have forced 16 turnovers, second in the Big Ten to Michigan State (18). Junior defensive backs Briean Boddy-Calhoun and Damarius Travis have two interceptions apiece. The secondary has been as good as advertised. ESPN.com named cornerback Eric Murray to its midseason All-Big Ten team (along with Wilson).

"You should be able to look at our defense and see Tracy Claeys' signature within it, enacted by his players, and how it responds," Botticelli said. "It's a level-headed, bend-but-don't break defense, which has served us well to this point in the season."

Opponents have gotten their yardage. The Gophers rank eighth in the Big Ten in total defense, giving up 349.8 yards per game. Opponents have converted on 38.7 percent of their third-down attempts, leaving the Gophers 10th in the conference in that category. And their 11 sacks are fewest in the league.

"I pay attention to two stats when the game is over, really three," Claeys said. "One is big plays, which we only allowed [Northwestern] one play over 20 yards. The other one is third downs, which we could have played a little better.

"But the ultimate stat still on defense is how many points you give up. Seventeen points — that's our goal."

There are big challenges to come. November brings Ohio State, Nebraska and Wisconsin — three of the Big Ten's top four scoring offenses. And for all their defensive flaws, Purdue and Illinois have been decent offensively.

Purdue senior Akeem Hunt rushed for three touchdowns against Michigan State after rushing for 177 yards against Illinois. And Boilermakers sophomore Austin Appleby has completed 39 of 57 passes (68 percent) the past two games. The Gophers say Purdue's offensive line will be a bigger challenge for the Gophers than Michigan's and Northwestern's.

"They have kind of a tough demeanor to them," Kill said. "Then they have two dynamic backs that are scary because if they break the crease, it's over with. They got it over against Michigan State. I think we all know how good Michigan State's defense is."

By season's end, the Gophers hope to be even better.