Sam Allardyce blamed West Ham's poor finishing for their shock last-minute defeat by Cardiff City.
Promotion favourites West Ham were in control for long periods but paid the price when Kenny Miller's turn and shot gave the visitors a 1-0 win.
"We've created numerous chances and today was one of those days when we were not clinical enough to punish the opposition," said Allardyce.
"We paid the ultimate price right at the very end."
Frederic Piquionne came closest to scoring when he hit the post, while new signing Matt Taylor was always a threat from set-pieces, testing Bluebirds keeper David Marshall on a number of occassions.
But, for all their pressure, the Hammers could not break through and Malky Mackay's men got their rewards for some stout defending when Miller, on debut, snatched all three points.
"I just hope it's one of those days," added Allardyce. "It didn't go for us, we've lost a game we really should have won.
"I told the players that you don't always get what you deserve but don't go and throw a game away, and that's what we've done.
"A point is not the end of the world after a good performance, it should have been three, but you get one and you move on.
"But we didn't even do that so it's a hugely disappointing day for everyone. As ever the expectation is high and we haven't lived up to that expectation."