Steve Cotterill suffered his first defeat in charge of Nottingham Forest as Aaron Mclean's strike earned victory for Hull at the City Ground.
Cotterill's men had won both games since he replaced Steve McClaren earlier this month, but the Tigers' triumph continued their fine away form.
The goal came in the 74th minute when former Forest captain Paul McKenna played Mclean through to beat Lee Camp.
Hull have now lost only two of their last 25 away games and are up to sixth.
Forest settled well, with Radoslaw Majewski and Marcus Tudgay threatening early on before Camp made a routine save when Tom Cairney shot from long range.
Wes Morgan headed straight at Adriano Basso in the Hull goal, and Basso produced the first meaningful save of the game in the 64th minute, tipping a 25-yard effort from Majewski round the post.
Hull substitute Dele Adebola caused his former club problems following his introduction from the bench just after the hour and he sent a low shot narrowly wide midway through the second half.
But the breakthrough game when Mclean latched on to McKenna's pass to beat Camp from close range.