Former Leeds forward Mallik Wilks produced a magnificent goalscoring display as Hull survived a late Ezgjan Alioski equaliser to progress on sudden death penalties.
Marcelo Bielsa sprang 11 changes to the side that fought tooth and nail with Liverpool at the weekend.
It was perhaps no surprise then, to see their opponent start the game the brighter and take an early lead inside the opening six minutes.
His left-footed drive took a deflection on route and left stand-in stopper Kiko Casilla with little chance as the deadlock was broken.
The game continued to offer up opportunities at both ends, with Wilks forcing a smart stop from Casilla, while Ian Poveda and Ezgjan Alioski both saw shots blocked.
Wilks continued to cause all sorts of problems throughout the half, but it was Leeds who should’ve found the game’s next goal minutes before the break.
Triangle of Cresswell, Davis and Casey in the middle have been given a really hard time by Hull's front line. Wilks' physicality and pace making him a handful. Bit more muscle in the middle would help. #lufc
— Phil Hay (@PhilHay_) September 16, 2020
The Whites won back possession in a advanced position, with Rodrigo latching on to a dangerous delivery into the box.
The Spaniard’s effort was again blocked by the spirited Hull defence, while Alioski’s off-balance volley from the rebound sailed high over the bar from 12 yards out.
The visitors were once again quicker out of the blocks following the restart, and continued to make life uncomfortable for Casilla.
A weak punch from a set-piece gifted an opportunity to Daniel Batty, but the midfielder blazed over under intense Leeds pressure.
Poveda then began to show glimpses of the talents that earned him a move to the club, with several mazy runs causing havoc down the right flank.
— Leeds United (@LUFC) September 16, 2020
A spell of relative comfort followed for The Tigers, however, with Bielsa cutting an increasingly frustrated figure on the touchline as the clock wound down.
James Scott spurned a glorious opportunity to put the game to bed, while Casilla continued his second half redemption after making late stops from Greg Docherty and Billy Chadwick.
With the full-time whistle looming, Leeds finally regained parity through Alioski.
The versatile 28-year-old hammered home after a Barry Douglas cross was nodded down into his direction to send the match to penalties.
Both teams scored four of their five penalties in regulation to send it to sudden death.
The drama continued to ratchet up as neither side looked like missing, with even Casilla himself scoring from the spot.
Jamie Shackleton ultimately saw his penalty saved with the scores at 8-8, with Alfie Jones then converting to send Hull through to the third round of the EFL Cup.