Two weeks ago, in the bowels of a Las Vegas casino, Senator Bernie Sanders of Vermont confronted the president of MSNBC, Phil Griffin, with a stern demand: Be fair to me.

Mr. Sanders, fresh off his victory in the New Hampshire primary, was fed up with what he considered unfair treatment by the cable network that is required viewing for many Democratic voters. He chided Mr. Griffin before abruptly ending their discussion, according to two people briefed on the exchange.

What a difference a Super Tuesday makes.

By Wednesday night, hours after Mr. Sanders suffered a string of defeats to his chief rival, Joseph R. Biden Jr., MSNBC viewers were greeted with the sight of Mr. Sanders sitting for a live interview with the network’s most influential host, Rachel Maddow, whose program the senator had avoided since July.

“Good to see you, Rachel,” Mr. Sanders said, grinning.

It was a striking turnaround by the senator, whose allies often hold up MSNBC as Exhibit A of the “corporate media” that Mr. Sanders likes to condemn. His campaign agreed to the Maddow interview after digesting Tuesday’s results, prompting the anchor to rush to Burlington, Vt., in time for the 9 p.m. broadcast.