Play-off hopefuls Derby lost a home League One game for the first time since early October when they were beaten 2-0 by Fleetwood.
The visitors stunned Derby in the 11th minute when Jayden Stockley's 25-yard volley came off the crossbar, hit Joe Wildsmith and bounced in.
Fleetwood were causing Derby problems every time they went forward and they scored again in the 30th minute with Carlos Mendes Gomes beating two defenders and smashing home a shot at the near post.
The Rams made two changes before half-time and another two at the start of the second to try and change the course of the match.
But Fleetwood came close to a third in the 67th minute before Wildsmith made a good save at his near post to deny Jack Marriott.
Lewis Dobbin had a shot charged down and Joe Lynch made a smart save to keep out a David McGoldrick shot in the 80th minute.
Lynch fumbled a Jason Knight drive but that was as close as Derby came to scoring as they remain fifth in the table, while Fleetwood move up to 12th.