Steve Bywater was pressed into action early on, saving a Tommy Smith shot and then tipping an Adam Bolder 'up and under' over the bar.
The warning duly served, Derby took the lead after Calum Davenport, trying to dribble his way out of trouble, conceded a corner which Inigo Idiakez planted on to Tomas Repka's head.
Michael Johnson, who replaced Ian Taylor in the Rams' line-up - the first time he hadn't started since January - reacted first at the far post to head the ball home for his first goal of the season.
Tom Huddlestone then tested Steve Bywater with a crisp volley before the Hammers restored parity.
A Luke Chadwick cross eluded Marlon Harewood but fell to Matthew Etherington; his half volley deflected wickedly off Jeff Kenna's hand to totally wrong foot Lee Camp.
This buoyed the Hammers, but shots from Chadwick, Teddy Sheringham, Harewood, and Carl Fletcher - via a deflection for a corner - all went wide before half time.
Derby had a let-off when Nigel Reo-Coker burst through, but his attempt on goal in a crowded box, with Camp beaten, was cleared off the line by Jeff Kenna.
Teddy Sheringham then had a shot cleared off the line by Mo Konjic, one of three Derby players on the line, after Harewood had cut the ball back to him.
Bywater then made a great close range save from Grzegorz Rasiak's header after Tommy Smith crossed from the left.
Shortly after Huddlestone was booked for a foul on Fletcher, Bobby Zamora came on for Teddy Sheringham, who passed the captain's arm band to Nigel Reo-Coker.
Zamora was then booked, when, after he chased a ball with Jason Talbot, the latter fell to the ground and Zamora caught him in the back.
Mo Konjic ran 25 yards to confront him - while Talbot, receiving treatment, theatrically rubbed his head - and also received a yellow card from Graham Poll.
Malky Mackay missed out on because of a calf problem and was replaced by Hayden Mullins, with Andy Melville added to the bench.
Tomas Repka went across to centre half with Hayden coming in at right back.
Chris Powell received a warm welcome at the club where he was player of the year in 1996/97.
Adam Nowland, who has had a groin problem of late, completed a loan move to Gillingham for a month.
TEAM: Bywater, Mullins, Repka, Davenport, Powell, Chadwick, Reo-Coker, Fletcher, Etherington, Sheringham [Zamora], Harewood.
Subs unused: Walker, Rebrov, Lomas, Melville.