The Sheffield side who had won five games in a row dominated but Forest, with keeper Paul Smith and centre-back Wes Morgan outstanding, held out.
Forest, fresh from a thrilling 3-2 win over Bristol City at the weekend were in trouble in the 15th midfielder. Greg Halford and full-back Kelvin Wilson squared up to one another in an off-the-ball incident and there was some pushing before the Forest defender headbutted Halford.
The lanky on-loan Sunderland player needed treatment as referee Michael Jones, who head earlier booked centre-back Ian Breckin for a rash challenge, red-carded Wilson.
The Sheffield side, undefeated in ten league games, struggled to find their rhythm, winger Dave Cotterill ballooning a long-range strike high over the bar, before Luke Chambers hacked the ball away from Jamie Ward six yards out.
Forest, holding out under intense United pressure, escaped in the 32nd minute, Halford was handed a half chance as he ran onto a Nick Montgomery cross but pulled his header over the top from ten yards.
Cotterill's free-kick was hacked away from Halford as United turned the screw.
Forest then failed to clear a Howard free-kick as Jamie Ward steered the ball back into the area but substitute Craig Beattie squandered the chance dragging his header well wide of the target.
Darius Henderson, quiet for most of the game forced an opening as he charged into the box with Breckin at his heels, but Smith was quickly off his line sliding into to hammer the ball clear.