United's women's SSE Women's FA Cup campaign ended in heartbreak after two late goals led to a penalty shootout defeat after a game which Carla Ward's side had largely controlled.
The first half was completely dominated by the visitors, former Villa forward Ebony Salmon proving a menace to her former team mates but the ball wouldn't fall for the Blades early on.
The goal finally came shortly before the half hour mark but it was another former Villa player, Maddy Cusack, who scored from close range for her first United goal.
The game then entered a stale period. Phoebe Warner had to go off after taking a knock to the head which ensured 10 minutes of first half stoppage time, before further treatment saw a 20-minute delay at the start of the second half.
When the action did finally get underway the hosts put plenty of pressure on the Blades but Salmon missed a big chance at the other end, the striker denied by Sian Rogers.
Salmon did get her goal soon after when she ran through and slotted into the corner and it seemed like that would be that for United, but Salmon was again thwarted soon after when through on goal looking for a third.
But with their first clear opening of the game, Jodie Hutton slotted past Davies to ensure a nervy last 15 minutes.
It seemed it would be United's day when Sophie Haywood blazed over with the goal gaping soon after and the game appeared to be wrapped up when Bex Rayner fired home from the edge of the box with six minutes to go.
But immediately after that United conceded a penalty which Hutton smashed down the middle to once again reduce the deficit to one.
And in the 96th minute, a free-kick launched forward was smashed onto the bar before it fell to Hutton who slotted home at the second time of asking to complete her hat-trick.
It meant extra-time and as both teams tired, chances were few and far between but United did go close when Tania Marsden hit the side-netting and Alethea Paul agonisingly hit the bar in the 118th minute.
As the game moved onto penalties, Paul's miss with United's first penalty proved decisive as Villa put away all five of their spot kicks to progress to the quarter-finals.
Blades: Davies, S. Barker, Tierney, Pennock, Cox, Gilliatt, Rayner (Ford 88), Paul, Sarri (Dixon 54), Cusack, Salmon (Marsden 90).