NCAA Tournament sets viewership record for first two rounds

March Madness delivered a first-week ratings surge, with the men's NCAA Tournament averaging 10.1 million viewers across CBS, TNT, TBS and truTV, making it the most-watched tournament ever through the first two rounds, according to Nielsen Big Data.

The opening round set the tone. First-round games averaged an all-time best 9.5 million viewers, up 9% from last year, before the round of 32 climbed again to an 11.0 million average, a 7% rise from last year and the most-watched second round since 1993.

The biggest spike occurred Sunday during the early prime-time window, when the combined audience reached 19.7 million -- the largest single first-week window on record. That stretch included St. John's late thriller over Kansas, Iowa's upset of top-seeded Florida and Tennessee's win over Virginia, a series of close finishes that kept viewers from flipping away.

The broadcasters hope the audience spike will carry into the next phase of the bracket, with the Sweet 16 scheduled to begin on Thursday. The weekend also set the stage for a conference-heavy second week, with Big Ten teams making up a large share of the remaining field (six of 16 teams).