The network's NCAA March Madness on Demand (MMOD) offering also saw a 71% jump in live video and audio streamed from Thursday to Sunday to 6.5 million hours, according to data released Monday by CBSSports.com. Television ratings were up 6%.

Thursday's opening-round coverage of the NCAA Men's Basketball Tournament via CBS' on-demand digital service attracted 2.7 million unique visitors, a 56% audience gain over last year.

CBS attributed the gains to media cross-promotion and the syndication of its MMOD video player to hundreds of Web and mobile outlets. The platform spans its own properties such as TV.com, Last.fm and GameSpot.com to partners in the CBS Audience Network and social networking sites including Facebook.

"Our success is being driven through a massive cross-platform marketing campaign that includes CBS Interactive's leading properties, promotion across CBS Corporate network television and radio assets and tremendous distribution from our partner sites in the Developer Platform," said Jason Kint, senior vice president and general manager, CBSSports.com, in a statement.

CBS has sold some $30 million in online advertising for the tournament, up 30% from a year ago. The network began offering live streaming of all 63 NCAA tournament games on the Web for free last year.

This year, the CBS debuted an MMOD iPhone app at $4.99 for the initial download. As of Monday, it was the second-most-popular paid program in Apple's App Store, highlighting the potential for paid live sports coverage via mobile devices.

In particular, it suggests a natural fit between special sports events, such as the NCAA Tournament or the Super Bowl, and one-off mobile apps that free cell customers from having to add a monthly video subscription just to catch a handful of big events a year.