Centre-half Lees was sent-off just after the half-hour mark for a dangerous high challenge on Jay Tabb, described by Warnock as a "ridiculous tackle".
Leeds had been the better team to that point, but they struggled to contain the hosts after the break and David McGoldrick's double and a third from Jay Emmanuel-Thomas ensured the visitors left Portman Road empty-handed.
"It's difficult doing a press conference when you think you should have won three or 4-0 and you've lost 3-0," said Warnock. "It's a crazy day and I can't believe we haven't won.
"We've got one lad who's let everyone down. He's let me down, the team down and all the fans who travelled here. It was one stupid moment. I don't know what else I can say, other than it was a ridiculous tackle.
"We were dominating. I've never been to Ipswich and dominated as much as that in my life and if I were Mick McCarthy I'd fill in a lottery ticket tonight."
Warnock conceded that his side cannot afford to drop any more points if they are to break into the play-off places by the end of the season.
"Mathematically, we're still going but it means we've got to win every game now," he said. "We put a great effort in but you need a little bit of luck - not stupidity like that.
"It's absolutely criminal that I'm sat here talking about a defeat and the lads aren't on the bus having clawed back points against the teams above us."