Clint Eastwood may be the last thing standing between social media and the Super Bowl.

An ad for Chrysler featuring Mr. Eastwood in Super Bowl XLVI told viewers it was "halftime in America" and urged Americans hurt by the economy to "make a comeback" because "our second half is about to begin." It was probably the best-recalled spot from last year's game. Yet Chrysler achieved this status by doing the opposite of what the modern Super Bowl advertising playbook advises marketers to do.

Rather than blast teasers of the commercial across YouTube, Facebook and umpteen other types of social media, Chrysler worked it up old-school, waiting until the Super Bowl itself to surprise and excite TV viewers with the actor and his message.

The automaker, which declined to comment for this article, may be one of the last of a breed. Beginning as early as this week, many advertisers in the Big Game will tease and reveal details of their Super Bowl creative as a means to generate response through digital and social media. Think about Honda's ad last year featuring Matthew Broderick reprising his role as Ferris Bueller, or GM's Chevrolet spot focused on a college grad who goes wild after thinking his parents bought him a car or Acura's funny spot starring Jerry Seinfeld. They were all over the internet in the days leading up to the game, and often in longer, funnier versions than those actually appearing on TV.

To be sure, harnessing the power of social media makes perfect business sense. When an advertiser shells out between $3.5 million and $4.5 million for a Super Bowl ad, using social media to get added exposure isn't just an afterthought. It helps amortize the cost of the commercial by generating millions of dollars in free publicity.

Audi of America, which is making its sixth-consecutive appearance in the event, believes chatter about Super Bowl ads begins to fade between 24 and 48 hours after the game is over, said Loren Angelo, general manager-brand marketing for the automaker. Unveiling the ads in the weeks before kickoff gives an advertiser the abiltity to have "a much longer conversation" with consumers, he said.

"The value is certainly in the anticipation of the Super Bowl," Mr. Angelo added. "There's only so much that people are going to talk about at the water cooler on Monday morning."

The technique threatens to put a favorite Super Bowl ad trick on the shelf to collect dust. For decades, Super Bowl ads hinged on "the reveal" or the delivery of something surprising. While this new era of ads is generating loads of digital and social response, they are also removing a lot of the shock and wonder that were once a big part of the experience. Would Apple's famous "1984" ad from Super Bowl XVIII have had as much impact if it were shared endlessly online in the weeks leading up to its official TV debut?

Some critics think the old ideas are more sound. "Last year's Super Bowl really calls the strategy of pre-release into question," said Charles R. Taylor, a marketing professor at Villanova Business School. With so many companies running visual teasers of their spots, he said, many advertisers lost "the element of surprise" and its absence "may have dampened the effectiveness of some pretty good ads that would have made a splash if not previewed."

Mercedes Debates

Mercedes-Benz, which is making its second appearance in the Super Bowl, has held many debates about whether to unveil its advertising ahead of time or keep everything secret, said Steve Cannon, president-CEO of Mercedes-Benz USA, and "I sort of skew toward that camp that says maximize impact." Making the ads available online tends to attract a smaller audience of diehards, he said, while the majority of game-day viewers "are seeing it for the first time and it's a total surprise."

Though it will run promotions on social media and at retail, Paramount Farms will keep a 30-second ad for Wonderful Pistachios featuring South Korean rapper Psy a secret, said Marc Seguin, VP-marketing. "It's exciting enough and visually has so much talk value. We want everyone to see it at once," he said. Likewise, Roy Benin, chief consumer officer for Mars Chocolate North America is fearful of bursting "the anticipation bubble," so the candy maker won't tip its hand on its M&M ad. "There's that first-time, premier reveal [in game] that we believe is compelling."

Many sponsors acknowledge they can't show up to the game without something else to say that hasn't already been digested by hundreds of thousands of video streamers. As Century 21 prepared to roll out ads in the Super Bowl last year, it released previews internally. "There's a balancing act," said Beverly Thorne, chief marketing officer.

Clint Eastwood isn't one for balance. He has always portrayed characters who definitively choose one side over the other. And his success in the 2012 Super Bowl tells us it's still possible to spark a national ad phenomenon by using Super Bowl Sunday and nothing else.

But it's a harder feat to accomplish -- and less certain, to boot. Harnessing social media is the easier choice. As marketers take the path of least resistance, however, they may permanently transform the Super Bowl ad experience, which has become a cultural institution itself.