Grant Holt scored twice in the first half, sandwiching an equaliser from Delaney, who was sent off in the 37th minute for a professional foul on Holt.
Keane's men rarely threatened an equaliser in the second half and, after Holt completed his treble in the 76th minute, substitute Wes Hoolahan added a fourth two minutes later.
Keane said: "It was a long afternoon for us, that's for sure. I thought at 2-1 down we were still in the game and causing them a few problems but the sending-off just before half-time changed everything.
"I'm not going to start criticising the officials, there's been too much of that recently. The ball should have been cleared, it's as simple as that and that was the case with the first goal as well. If we'd done our jobs properly there wouldn't have been a problem.
"If you defend like that you are not going to win many games of football. We made it hard for ourselves and Norwich are a good side who took advantage of it. We haven't been winning many games with 11 men recently so it was always going to be tough with just 10."
Source: PA
Source: PA