Updated

By Samuel P. Jacobs

(Reuters) - Legendary Boston baseball venue Fenway Park has been a theater of drama and heartbreak for Red Sox fans in its century-long history, but this year it is entering a whole new league.

Major League Baseball's old jewel has become the hottest prop of the political season, gracing the campaigns of Republican presidential front-runner Mitt Romney and local Senator Scott Brown, and hosting one of the nation's top political talk shows.

Fenway Park celebrates its 100th birthday on Friday, an occasion that team brass and the city of Boston have been marking all spring.

To coincide with the anniversary, Romney and wife Ann gave an interview to Diane Sawyer of ABC television in a Fenway sky box overlooking the field, selecting the ballpark as the scene for the first network interview of his general-election campaign.

Wearing jeans and a striped button-down shirt, the former Massachusetts governor toured Yawkey Way, a street outside the stadium, with Sawyer and members of his family.

Later, Romney took a seat along the third base line in the stadium known for its tight angles and obscured views. He watched the Red Sox lose to the Tampa Bay Rays, hosting two donors to his campaign.

That Red Sox owner John Henry, who once campaigned for John Kerry and has given hundreds of thousands of dollars to Democratic causes, opened the ballpark to the Republican for an interview showed a spirit of bipartisanship.

Not everyone was pleased, or convinced of Romney's credentials as a member of the Red Sox faithful.

"It was probably the first time he's been there," said former Massachusetts governor and 1988 presidential candidate Michael Dukakis. "In jeans of all things," the Democrat said with a sigh.

"Oh, Red Sox, I'm afraid," Romney said. "I've lived in Massachusetts for 40 years."

But he also gave a nod to the Detroit team, in the kind of comment that has earned him a reputation for being too keen to see both sides of an argument.

"I grew up a Tigers fan, of course," Romney said.

He is not alone in flaunting sports affiliations. His autumn opponent, President Barack Obama, openly fills out a bracket for the annual U.S. college basketball tournament, selecting the teams he thinks will win. He also openly roots for his hometown Chicago White Sox.

POLITICS AND RED SOX

In tribute to Fenway, the hosts of MSNBC's morning political talk show "Morning Joe" will broadcast live from there on Friday.

"If you're born in this town, you are infected with two things: politics and Red Sox," said Dukakis.

One appears to be charging over the other this spring. The high-profile U.S. Senate race, pitting Republican incumbent Scott Brown against Elizabeth Warren, a former adviser to Barack Obama and progressive favorite, has only added to the competition.

As the baseball season began this month, Brown released two different ads heaping praise on the ball club and its home.

"You know, lots of things have changed over the years but not Fenway Park. Think of it. The park opened in 1912, the same year as the sinking of the Titanic. It is not only the home of the Red Sox. It also connects us to our past," Brown said in a radio advertisement.

Later, the campaign released a video of Brown and his wife walking around Fenway on Opening Day. Despite the team's top-dollar payroll and two World Series wins in the last 10 years, Red Sox fans still see themselves as underdogs. It's a label Brown, who won a shocking upset in 2010 to take Ted Kennedy's seat, seeks to claim for himself too.

"Listen, I'm an optimist. I'm a Republican from Massachusetts," Brown says in the video.

Warren, whose Oklahoma roots prevent her from being a Red Sox fan by birth, hasn't been far behind. Her campaign released a photo of the candidate with her husband taking in Opening Day. Recently, she shared her predictions on Twitter for the team's wins (96) and most valuable player (outfielder Jacoby Ellsbury) this year.

Warren, who Brown portrays as an elitist, can burnish a populist image by rooting for the hometown team.

"I think she is protecting her flank," said public relations executive Thomas O'Neill, who used to go to games with his father, Tip O'Neill, the former U.S. House speaker.

But what Fenway Park gives, it can take away.

Romney stumbled last year when he said he had "no idea" that Red Sox rival Tampa Bay played under a dome. (The Red Sox have played more than 100 games at the domed Tropicana Field.)

In a December forum, Warren failed to name the years of the last two Red Sox championships. In an interview last summer, she said it was her husband who was the Red Sox fan in the family.

And over the years, Fenway's age has often led to call for a new stadium. Brown drew some jeers from the press box for saying in his radio ad that moving the Red Sox out of Fenway would have been a mistake, without noting his past support for relocating the squad.

This week, Brown received a razzing from the Boston Herald for cashing a check from The York Yankees president Randy Levine. Brown said he would keep the money. The Herald wondered, "What's next, a Derek Jeter endorsement?"

(Editing by Alistair Bell and Philip Barbara)