Steve Bruce's men delivered a dismal first-half display against play-off chasing Derby, prompting the introduction of Gedo, a recent loan signing from Al Ahly, and Nick Proschwitz at the break.
Gedo, who also came off the bench against Brighton at the weekend, headed Hull in front within 90 seconds of his half-time arrival.
However, after both sides had struck the woodwork, Jamie Ward looked to have rescued a point for the Rams when he capitalised on an error from City goalkeeper David Stockdale to level with six minutes remaining.
There was still time for Elmohamady to have the final say with a downward header from Robbie Brady's corner, and Derby finished with 10 men following Gareth Roberts' 89th-minute dismissal for a late tackle on Proschwitz.
- Sports & Recreation
- Nick Proschwitz