"The Sun Backs Blair", its front page shouted from news-stands today. In an editorial it said the Labour leader is the "breath of fresh air" Britain needs and that the Tories are "tired, divided and rudderless" and no longer deserve support.
"This is the election for the millennium," it said. "In six weeks' time Britain will vote for a government to take it into the 21st century. The people need a leader with vision, purpose and courage who can inspire them and fire their imaginations. The Sun believes that man is Tony Blair."
Last night the editor, Stuart Higgins, told Channel 4 News: "I believe that we are saying something that our own readers believe. We are supporting Mr Blair because we see him as a dynamic, exciting, energetic new leader for this country."
This decision, from a paper which has backed the Tories for 20 years and was vehemently anti-Labour at the last election, will come as a big boost for Labour and a blow for the Conservatives. A Conservative Central Office source said last night: "It's not editorials which count, but the votes of millions of Sun readers. We believe that they understand the benefits they are now enjoying by working with this government. They will prove the Sun wrong on election day."
The Sun's support for Mr Blair came the day after the Labour leader, in an article in the same newspaper, known for its Euro-sceptic views, toughened his stance on Europe.
"New Labour will have no truck with a European superstate," Mr Blair wrote. "A single currency will not be imposed on the British people. Their consent is paramount."
The Times, a sister paper to the Sun in Rupert Murdoch's News International stable, said today it will also "declare a preference" but closer to polling day.
It remains to be seen whether all the Murdoch papers, which include the Sunday Times and the News of the World, will back Mr Blair.
It is no secret that the relationship between Mr Murdoch and Mr Blair has grown in recent years - in July 1995 Mr Blair addressed the media magnate's three-yearly management conference in Australia.
However, Labour last night strongly denied that the party and Mr Murdoch had struck a deal over the election campaign.
Save for the Mirror, a Labour stalwart, this morning's other national newspapers were reserving judgment until more of the parties' arguments have been aired.