Not only was the tie virtually over at 2-0 but the required work rate and desire was absent also.
"I am very, very disappointed with the start we had," Keegan told Ananova. "At half-time, in all my time in management, I don't think I have ever been more angry with some of the players, although not all of them.
"We were not committed to winning tackles or challenges and 50-50s became 70-30s for them and that is very disappointing.
"I'll put up with the defeat we had against Middlesbrough on Sunday because we were terrific and scrapped and worked for each other and were unlucky, but I can't put up with the way we played in the first 25 minutes here."
The lashing had some effect with Keegan's men coming out the stronger side and finishing with more shots on goal and corners.
Robbie Fowler's header gave the Blues a lifeline on 80 minutes but as City pressed for the leveller, the hosts broke clear and sub Fredi Kanoute put the result beyond doubt.
"We got the spirit together in the second half but it was too late," said Keegan.
"You can't give Tottenham or any team a 2-0 start and we were left playing for pride."