Rarely can political speeches at conference be described as "game changers".
But there can be no one in this hall in Manchester, including the critical members of the press, who thought that Ed Miliband's speech was anything other than a triumph.
Well delivered. Coherent. Authoritative. Relaxed. Personable. Funny. Captivating.
If I were one of David Cameron's advisers right now I'd be a little worried.
And remarkably, he did it all over the space of 65 minutes without an autocue. Without a single note.
There were many doubters (including some in his own party) about Ed Miliband's style of leadership.
His case has not been helped by the fact that polls show, as they did again this morning, that the party he leads is much more popular than the man who leads it.
To put it bluntly: few people could see him as a future Prime Minister.
By 3.30pm this afternoon, all that had changed.
He did it - not by setting out policy (that blank sheet of paper still does not have much writing on it) - but by earning the right to be heard.
He may have overplayed the comprehensive school point. He may have said "One Nation" one too many times. But he took apart the government. Made the case for change. Ridiculed not just one - but several members of the Cabinet and had the audience here jumping to their feet in adoration.
He hit the right spots: NHS; education; income tax; banks.
Above all else he has cemented his position as the leader of the Labour party - and built a solid platform on which to build his case before the next election in 2015.
He needed to do well here because Labour's job is only going to become more difficult if, as the evidence currently suggests, the economy pulls out of recession.
What is good for the economy is not always good for the Opposition.