The ACC held serve Saturday, with Clemson safely navigating around its biggest obstacle on its journey to the College Football Playoff.

The Big 12 and SEC essentially swapped hopefuls with Oklahoma State pounding TCU and Alabama hammering LSU.

The Pac-12 stayed put, everybody waiting for the Stanford-Notre Dame elimination game Nov. 28.

Four unbeatens lost on Separation Saturday, but the biggest loser was the Big Ten, which saw one of its playoff contenders lose in a most controversial manner.

Michigan State debuted at No. 7 in the CFP rankings last week, and the countdown began to the Nov. 21 collision in Columbus, which figured to be the Big Ten’s game of the year: unbeaten Ohio State vs. unbeaten Michigan State, perhaps with both teams ranked in the CFP Top 5.

Nebraska’s upset of the Spartans has taken the shine off that showdown.

It also has hurt the Big Ten’s bid for a spot at the final four table.

The committee’s initial rankings hinted at the Big Ten’s potential problems.

Ohio State, the undefeated defending national champion, debuted at No. 3 last week despite being ranked No. 1 almost the entire season in the AP Poll and every week in the Coaches Poll.

It remained No. 3 in the playoff poll this week.

Perhaps the committee’s perceived slight was acknowledgment of the Buckeyes’ weak nonconference schedule.

The message, intended or perceived, is the Buckeyes don’t have a lot of wiggle room.

Michigan State’s loss means the Buckeyes no longer have any.

Ohio State can’t lose to a one-loss team this late in the season and feel assured of being selected to the final four.

Worse for the Big Ten, it can’t feel real comfortable that any one-loss team would get an invite. A one-loss Iowa team, for instance, with no notable nonconference wins, would be a difficult sell even if it beat an undefeated Ohio State in the Big Ten title game.

The rankings will continue to change as contenders play contenders. But it’s certainly possible, if not likely, that Clemson finishes undefeated. One Big 12 team, Baylor or Oklahoma State, could do the same. Alabama looks like a good bet for the third spot, leaving as many as six contenders vying for the fourth.

The Michigan State-Ohio State winner, assuming it also won the conference championship, seemed destined to be that team.

Now, there is no such guarantee if one-loss Michigan State hands the Buckeyes their first loss — all because of a late, questionable touchdown pass thrown by a team best known for its rushing attack.

Nebraska’s win was great for Nebraska but potentially a very big loss for the Big Ten, the biggest setback for any of the Power 5 conferences.