Rotherham ended Coventry's unbeaten start to the season in emphatic fashion with a 4-0 victory at the New York Stadium.
Matt Crooks struck twice for Rotherham either side of two Michael Smith penalties as the Millers ran riot.
Coventry skipper Kyle McFadzean had a day to forget for the visitors, playing a part in giving away both spot-kicks as well as being sent off.
The hosts were in front after 13 minutes as Crooks' header was too powerful for Marko Marosi to keep out.
The lead was doubled in the 19th minute when Michael Smith fired home from the spot after he had been tripped by Marosi following a horribly short pass from McFadzean.
Jake Hastie could have made a bad start even worse for Coventry but he was denied by Marosi and the rebound from Crooks was kept out.
Rotherham did add a third goal in the 58th minute, though, when Smith netted his second penalty of the game.
McFadzean gave it away after bringing down Crooks clumsily and he was duly sent off by referee Darren Handley.
Another defensive mix-up led to Rotherham's fourth goal in the 75th minute, with Crooks poking beyond Marosi after Michael Rose switched off with the ball at his feet.