Purdue coach Jeff Brohm spent all week searching for a weak link in Michigan's defense.

He's still looking.

Yes, even for someone who possesses a creative offensive mind like Brohm, facing No. 8 Michigan on Saturday will be his toughest test yet as the teams open Big Ten play.

"Early in the week you watch, you're like, 'Holy cow, how are we going to score a point?' I'm at that stage right now," Brohm said. "We're going to have to continue to study hard, try to figure something out. They're very good."

Brohm didn't need the game tapes to show it.

The national rankings prove it, too.

After finishing with the Football Bowl Subdivision's top-ranked defense in 2015 and 2016, the Wolverines returned just one starter this season — and haven't fallen off much.

The Wolverines (3-0) are ranked No. 5 overall (208.0 yards per game), No. 9 against the run (82.3), No. 12 against the pass (125.7) and No. 24 in points allowed (14.7). They're sixth in sacks (4.33 per game) and second in defensive touchdowns (three).

Now, finally, Michigan's defense will get a chance to show the rest of the league just how good it really is.

"I can't wait," defensive end Rashan Gary said. "It's opening up Big Ten play for us and everybody can't wait to attack it. It's a big week for us."

This game might be more challenging than Michigan or anybody else initially anticipated.

Brohm's rapid rebuild has energized the program and the fan base for the first time in years. The result: Ticket sales are soaring and Wolverines coach dubbed Brohm the early front-runner for Big Ten coach of the year.

The Boilermakers (2-1) posed a tougher-than-expected challenge against Louisville, easily beat Mid-American Conference contender Ohio and last week pulled off a 32-point win at Missouri . Michigan won't be an easy opponent for the signature win Purdue needs.

"Those defenses, you're probably not going to be able to work the ball down the field," Brohm said. "You're going to have to find a way to make a big play here and there to spark you, get something going, otherwise you're going to be punting real fast. Right now I have to let the optimism build, watch some more, figure out a few more things. But they're talented."

Here are some other things to watch:

COACHING FIRST

Brohm and Harbaugh have a lot in common. Both grew up with football-coaching fathers, both excelled playing at major colleges, both played in the NFL and, of course, both went on to become successful college coaches. This is the first time they'll go head-to-head on the football field.

RARE GEM

Saturday's game will be the first between these longtime rivals since 2012. They won't meet again until 2020 because of a scheduling quirk. When the Big Ten began division play in 2011, Purdue and Michigan wound up on opposite sides. When the conference realigned in 2014, the Wolverines wound up in the East while Boilermakers landed in the West. The five-year break between games is the longest in this series since the schools took a break from 1952-61.

LEADERS AND...

Purdue's Cole Herdman is averaging 28.6 yards per catch — the best among all Football Bowl Subdivision tight ends. Boilermakers quarterback David Blough is 17th nationally in passing efficiency (174.5) and punter Joe Schopper is No. 4 with an of 48.8 yards. None of Schopper's 12 punts this season have gone into the end zone, either. Schopper will be kicking to Donovan Peoples-Jones, who is No. 13 in punt return average (16.3 yards). Michigan's Ty Isaac is No. 18 in rushing yards per game (112.0) while kicker Quinn Nordin is No. 1 in field goals per game (3.67) and No. 6 in scoring (14.0).

SELLOUT?

Purdue's home crowds had been steadily dwindling until this season. Now the Boilermakers could have a sellout on homecoming weekend. In the 48 hours following the Missouri win, school officials said they sold an additional 3,000 tickets and as of Wednesday afternoon, only 5,000 remained for the game. Purdue hasn't had a sellout since the final home game for former coach Joe Tiller, in 2008.

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