Marlon King scored twice to dent 10-man Millwall's play-off bid and end their six-game unbeaten run with a 2-1 win.
Coventry, who are still not mathematically safe from relegation, took the lead through King in the early stages only for Andros Townsend to drill home an equaliser in first-half injury time.
Millwall substitute Neil Harris was on the pitch for less than two minutes before he saw red for an off-the-ball incident with Aron Gunnarsson.
And King made the most of the Sky Blues' man advantage with his 12th goal of the season.
The result leaves the Lions four points off sixth-placed Leeds.