Millen's View: Sheffield United away 2-3
City led 1-0 until five crazy minutes before the break, where the Blades scored two quickfire goals either side of a Nicky Maynard red card.
Millen responded at half-time by making a treble change and was seething at his team's first-half performance.
"That's the angriest I've been at half-time," the City gaffer told reporters.
"I couldn't believe the first-half performance and if I could have, I would have changed all eleven players, not just three.
"We had no energy or work-rate about our play and that's the first time I've accused our players of not giving everything.
"We were gifted the opening goal but there was nothing much else in it from our point of view.
"The manner of their first goal summed it up really and the second was unstoppable after Nicky Maynard's sending-off.
"Their sending off evened things up and allowed us to level from the penalty spot. Even then we failed to deal with a free kick into the box - like we had all day - and it cost us at the end."
Millen also admitted that he is unlikely to appeal Maynard's dismissal, meaning the ex-Crewe striker will serve a three match ban which ends his season.