Michigan State doesn’t have a championship-level secondary, and that fact couldn’t have been better exemplified than it was during Saturday’s 40-29 loss to Purdue.

Aidan O’Connell threw for more than 500 yards for the Boilermakers, with favorite target David Bell topping 200 yard receiving.

The Spartans, 8-0 and No. 3 in the CFP rankings coming in, have now given up 942 passing yards the past 2 weeks. They simply couldn’t defend a pass vs. the Boilers, who entered Saturday with a pair of wins against top-5 opponents during the past 3 seasons. All types of passes — short, bubble, intermediate, long-ball — ended up in conversions for Purdue, which never trailed during its home romp over a Big Ten heavyweight.

O’Connell was nearly flawless, completing 10-of-13 passes for 149 yards and 2 TDs in the first half. He continued his efficiency during the second half, finishing with a line of 40-for-54, 536 yards and 3 touchdowns. O’Connell’s yardage was the most by any QB vs. MSU and the most by any Big Ten QB this season.

Bell, one of the best WRs in the country, absolutely wreaked havoc on the Spartans’ B1G-worst pass defense, coming up with 53-, 50- and 42-yard receptions — huge plays that fueled the Boilers’ upset victory. His 42-yarder was vs. Chester Kimbrough, who’s had a difficult season in regard to coverage.

Garrett Miller had a 16-yard catch in the first half. Broc Thompson had an 8-yard TD reception, covered by MSU DBs Charles Brantley and Angelo Grose. Both of them were torched Saturday.

O’Connell and the Boilers did what they wanted through the air, proving that the Spartans have work to do if they want to be a real-deal contender in the Big Ten.

The Spartans’ season isn’t over, but their chances of making the College Football Playoff have been diminished a great deal.

Here is a look at some of the plays that caused coach Mel Tucker’s Spartans to stumble.

In the first half, true freshman kicker Stephen Rusnak missed a 42-yard field goal, points which the Spartans desperately needed.

Simeon Barrow, DL, was called for targeting early in the 3rd quarter on O’Connell, a momentum-shifting play that certainly inflated Purdue’s confidence.

Michigan State had a glimmer of hope, though. Running back Kenneth Walker III burst in for a 14-yard TD late in the first half, scoring with 1:09 to play before the break. At that point, MSU was down 21-14 and looked like it could fight back.

In the second half, and with a win just a few series away, Purdue converted on a 4th-and-1, with O’Connell completing a short pass to Bell, who lit up MSU with 11 catches for 217 yards and a touchdown.

It wasn’t unexpected. Michigan State was ripe for an upset. Purdue’s passing game pulled the curtain back and showed exactly why the Spartans won’t finish among the nation’s top teams — they can’t defend the aerial assault. One week ago, Michigan QB Cade McNamara threw for a career-high 383 yards. Every QB, just about, has had a nice stat line vs. the Spartans this season, making for a problematic forecast.

If a team can throw, MSU is beatable.