East Lansing — It was almost a year ago when Pat Narduzzi was named the head coach at Pittsburgh.

It was inevitable the architect of one of the top defenses in the nation would eventually leave Michigan State. Along with coach Mark Dantonio, Narduzzi helped the Spartans finish in the top 10 in the nation in total defense in four straight seasons — the only team to do so.

To look at it simply as the work of Narduzzi, however, would be unfair — unfair to those who had worked with Narduzzi and Dantonio for eight straight seasons at Michigan State and three before that at Cincinnati.

Still, when Harlon Barnett and Mike Tressel were promoted to co-defensive coordinators last season during the week of the Cotton Bowl, some wondered if they could continue the momentum. Would Michigan State continue to be known for its punishing defense, the one that finished in the top 10 in rushing defense for four straight seasons, the one that ushered in the “No-Fly Zone” and produced two cornerbacks that went in the first round in the NFL draft in consecutive years?

Sure, Barnett and Tressel knew the system front and back, Barnett as the defensive backs coach and Tressel as the linebackers coach. Even so, there was going to be an adjustment.

Both knew it wouldn’t happen overnight.

“(It was) getting adjusted to new coordinators, even though the system was the same and all those type of things,” Barnett said last week. “But they have to get adjusted to Mike and I doing it, as well, and I think they have. I think they have.”

It took some time, but they sure have.

After nine weeks of frustration and defensive play that felt foreign to the Spartans, it’s the defense that has been the spark down the stretch that has led Michigan State to its matchup with Alabama in the Cotton Bowl.

It’s as if the 39-38 loss at Nebraska in the ninth week of the season flipped a switch — no longer could the Spartans be pushed around. They needed to take control of games.

“I think it’s the intensity and the consistency for the whole 60 minutes,” junior linebacker Riley Bullough said of the defense’s transformation. “Before, in all the games leading up to and including Nebraska, we were playing pretty well but we would have one or two plays, or three plays, where we’d mess up a little thing and it would cause a big play. We’ve eliminated those and that makes a big difference.”

The numbers prove Bullough correct. Over the last four games, the Spartans have been a far different unit — almost resembling the outstanding 2013 and 2014 teams. They are allowing only 12.5 points after giving up 24 a game in the first nine games while the yardage numbers have plummeted, as well.

Michigan State has given up 91.8 yards a game rushing the last four games after giving up 122.6 in the first nine games, while the passing yardage allowed has dropped from 249.8 a game to 185. And the third-down conversion rate has gone from 38 percent to 28.

There were also big performances in the biggest games. Michigan State held Ohio State to 132 total yards, the fewest ever by an Urban Meyer-coached team. And in the Big Ten championship game against Iowa, it gave up only 52 rushing yards and created three turnovers.

“Good for them for coming together at the right time,” Barnett said. “November is a month for contenders, we all know that, and as we continue through the playoffs and those type of things, they know that this is our time. This is our time. Let’s get it done.”

The reasons for the turnaround go beyond just a mindset, however. One of the biggest reasons things have started to look more like a typical Michigan State defense is stability in the secondary.

There were questions entering the season — namely replacing cornerback Trae Waynes — and it didn’t take long for the revolving door of players to begin. Junior cornerback Darian Hicks was limited early after dealing with mononucleosis in preseason camp and later in the season suffering a concussion. And redshirt freshman cornerback Vayante Copeland suffered a fractured vertebrae in Week 2 that knocked him out for the season.

Add in the torn biceps for fifth-year senior safety RJ Williamson in the Big Ten opener and there have been seven different starting combinations. Those have included three true freshmen — safeties Khari Willis and Grayson Miller as well as cornerback Tyson Smith.

“We said last summer, a championship team is only as good as its backups, and we found that out this year, for sure,” Barnett said.

After Nebraska, however, things started to turn around. Hicks returned for the Maryland game and was starting the next week at Ohio State. Combined with the resurgence of sophomore safety Montae Nicholson, moving junior Demetrious Cox from cornerback to safety and the steady play of fifth-year senior cornerback Arjen Colquhoun, the secondary started to come together.

Finally, the Spartans were healthy again.

The solidified back end energized the entire unit. There were five turnovers against Maryland, including a pick-6 from Bullough, then the domination of Ohio State. Against Penn State there were four more turnovers and another pick-6, this one for defensive tackle Malik McDowell.

“I think we’re jelling more and all of our components are back, which is huge,” fifth-year senior defensive tackle Joel Heath said. “Once everybody was confident and injury-free, we played our best game. We understand what we have and are confident we can do anything.”

Whether that includes a win over Alabama remains to be seen. The Crimson Tide enter the Cotton Bowl with the third-best rushing attack in the nation, led by Heisman Trophy winner Derrick Henry.

But the Spartans, who now rank seventh in the nation in rushing defense (113.1) believe they are peaking at the right time.

“I think this whole season has been a testament to our program,” Colquhoun said. “We have had a lot of successes and four of our wins have been huge for our program. We have separated ourselves and have become an elite group. It has been an opportunity to prove Michigan State.”

And prove that defense is still its calling card.

Cotton Bowl

Alabama vs. Michigan State

Kickoff: 8 p.m. Dec. 31, AT&T Stadium, Arlington, Texas

TV/radio: ESPN/WJR

Records: No. 2 Alabama 12-1, No. 3 Michigan State 12-1

Line: Alabama by 10

Series: Alabama leads 1-0