Rudy Giuliani was accused of the ultimate flip-flop in the US presidential race yesterday after he backed the arch rival of his beloved New York Yankees to win baseball’s World Series.

The shocking declaration of support from the former Mayor of New York for the Boston Red Sox was denounced as a craven attempt to win votes in the crucial first primary in nearby New Hampshire.

Mr Giuliani, right, the Republican presidential front-runner, is a lifelong Yankees fan. He keeps a sign on his desk boasting that he is “Yankee Fan-in-Chief”. For him to endorse the arch rival Boston Red Sox is like a Liverpool fan backing Manchester United to win the Cup Final.

The announcement was met by a headline in the pro-Democrat New York Daily News declaring “Traitor!”

“He is not just a fan. He is a fanatic,” Doug Muzzio, a politics professor at Baruch College in New York, said. “In terms of its political impact, I think it’s very little, but as a lifelong Yankee fan, I find this to be the ultimate flip-flop. Is nothing sacred?”

The rumpus has proved particularly embarrassing for Mr Giuliani because he has often ridiculed Hillary Clinton, the Democratic front-runner, for becoming a Yankees fan when she moved to New York to run for the Senate. In a recent campaign speech, he quipped: “We do agree on one thing. We’re both Yankees fans. She became a Yankee fan growing up in Chicago. I became a Yankee fan growing up in New York.”

Mr Giuliani is running for the presidency on his record in New York, particularly his performance during the World Trade Centre terror attacks in 2001. But the New York native has taken pains to distance himself from the city’s reputation as a bastion of liberal politics.

“I got elected and re-elected honestly not because the people of New York City agreed with my ideas,” he recently told Republicans in South Carolina. “They didn’t. They agreed with my results. You agree with my ideas.”

Mr Giuliani’s declaration of support for the Red Sox came on the day he filed the paperwork for the New Hampshire primary, the first statewide ballot in the presidential race. He sparked wild applause by telling a Boston audience that he was backing the team in the seven-game World Series contest against the Colorado Rockies that began last night.

He denied that he was playing baseball politics to win votes. “In Colorado, in the next week or two, you will see, I will have the courage to tell the people of Colorado the same thing: that I am rooting for the Red Sox.”

The archetypal New Yorker explained that, after the Yankees were knocked out, he always backed the team that played in the same league. “Somehow it makes me feel better if the team that was ahead of the Yankees wins the World Series, because then I feel like, well, we’re not that bad,” he told reporters.

Mr Giuliani is leading the Republican race by 32 per cent to Fred Thompson’s 15 per cent, with John McCain and Mitt Romney following close behind, according to polls.

Mr Thompson was quick to denounce Mr Giuliani. “We thought Mayor Giuliani’s endorsement of Democrat Mario Cuomo \ was rooting for the other team,” he said. “But for Yankees fans, this might be a new low.”

Baseball has become a potent political tool in the campaign. Candidates use it to mould an image of being “regular people”, but it has its pitfalls. Mrs Clinton was asked at a recent debate whom she would support if the Chicago Cubs (her hometown team) played the Yankees in the World Series. “I would probably have to alternate sides,” she replied, a diplomatic but politically expedient answer.

Barack Obama, responding to Mr Giuliani’s comment, told an audience in Boston: “I am a \ White Sox fan.” After the inevitable boos, he delivered his punchline. “You don’t want somebody who pretends to be a Red Sox fan as President of the United States. You want somebody who is a principled sports fan.”

East Coast rivalry

— Lou Gehrig got the most home runs for the Yankees in a single game, winning four in 1932

— Joe DiMaggio has the highest right-hand batting average – 0.381

— In 1920 Red Sox star player Babe Ruth was sold to the Yankees, who went on to win 26 World Series championships while the Red Sox failed to win any for the remainder of the century

— In 2004 the Red Sox finally won the World Series, breaking what was called the Curse of the Bambino

— In 1947 Jackie Robinson was the first African-American to play in the major leagues.

— Ted Williams has the highest batting average and in 1941 was the last major league player to hit at least 0.4 hits for every ball faced.

— The team have the most no-hitters thrown by a major league team – pitches thrown preventing the opposing team from achieving a single hit in an entire game

— Rookie, Clay Buchholz, 23, is one of only three pitchers since 1900 to throw a no-hitter in his first or second major league game.

Sources: Times database, http://boston.redsox.mlb.com, newyork.yankees.mlb