A lively Yorkshire derby saw Hull strike twice in quick succession through Matty Fryatt and James Chester at the KC Stadium, only for a Robert Snodgrass gem to bring United back into contention before half-time.
Davide Somma powered in a second-half leveller, but both teams struggled to bring a fitting finale to an intriguing tie.
Hull kept the same XI that drew with QPR, as Leeds made two changes.
Grayson's charges had enjoyed 10 days' rest prior to the clash, which allowed Andy O'Brien to shake off a hamstring problem and replace Leigh Bromby at centre-half, while Somma came in for Sanchez Watt.
That breather may have left the United backline rusty as they were exposed after 30 seconds.
James Harper and Fryatt combined to release the latter and when his low cross picked out the unmarked Aaron Mclean, a goal seemed certain - although the former Peterborough man somehow bundled wide from a matter of yards.
Leeds recovered to shrug off any lethargy and Max Gradel curled a shot over the bar in his team's first attack of note.
From there, the Whites' confidence grew. George McCartney tested Brad Guzan with a 30-yard drive and Bradley Johnson cleared the bar with a header from the following corner.
Leeds thought they had scored when Snodgrass' drive, palmed up by Guzan, nearly looped in before it was retrieved by the American keeper.
Hull responded as the pace was thrust up a notch. Only Kasper Schmeichel's fingertip save denied Robert Koren a spectacular strike and the Dane was at his sublime best again moments later to thwart Anthony Gerrard, with his header destined for the top corner.
Set-plays and long-range strikes had offered the best hope of breaking the deadlock.
But in the end, it was a simple, three-pass move that proved decisive. James Chester carried the ball out of defence to feed Mclean, who was allowed to turn.
He played in Fryatt, who slipped between the Leeds back four to slot past Schmeichel and put Hull ahead after 32 minutes.
And with Leeds unsettled, the Tigers pounced to double their advantage six minutes before the break when Chester planted home a header from Andy Dawson's corner.
However, City couldn't keep the score at 2-0 until half-time as Snodgrass put a peach of a free-kick around the wall and past Guzan.
Leeds needed to regroup for the second period and within 10 minutes they had levelled, Somma's thunderbolt carrying over the line after it cannoned off the underside of the bar.
Grayson's side passed the ball confidently thereafter but could not manoeuvre past the home side and a lull ensued.
That was broken by substitute Lloyd Sam hacking a Fryatt header off the line after both managers made changes in search of a winner.
Gradel was shut down when well poised but the game petered out to finish level as Hull ended the night with 10 men, Liam Rosenior stretchered off.