The first primary debate ever held in Nevada was a hit for CNN with more than four million total viewers watching. CNN says it's the highest-rated primary debate in recorded history.

Moderated by Wolf Blitzer with questions from Campbell Brown, John Roberts, and the audience, the debate began like a rock concert, with the candidates being announced one-by-one onto the stage. CNN/U.S. president Jon Klein says what came next, is what kept viewers tuned in. The debate "didn't have the gimmicks," Klein tells TVNewser. "No speed round, no clock, no artificial time limits" on the candidates.

And no doubt, a spike in viewer ship due to Sen. Hillary Clinton's critically panned performance in Philadelphia two weeks ago. How would she fare on this night? On that point, Klein says, "the horse race gets them in the tent, but it's not going to keep them there."

The debate was also Campbell Brown's bow at CNN. Klein calls it a "smash debut" for the former NBC News anchor. Klein also credits the team of DC VP David Bohrman and political director Sam Feist who "continue to come up with innovative new formats...it's tough to breath new life into a old format, but they've managed."

Up next for CNN, the GOP YouTube debate Nov. 28. I asked Klein if he thought the viewer interest would be as high on that night. With its "barrage of questions from ordinary people," Klein thinks it could be. Especially because of the "trepidation from Republican candidates." We'll see.

For now, CNN will spend its Vegas winnings wisely. "I think the numbers prove what works and what doesn't," says Klein. "Depth, substance and real news. That's what viewers expect and that's what we're delivering."