Clark had to be on red alert for United moments before the half-hour after a clever João Pedro ball almost released Ken Sema, but then down at the other end Bachmann was forced into a good stop as Iliman Ndiaye beat Kamara before firing from a tight angle.
The Hornets went close to taking the lead with little over three minutes left of the first 45 when João Pedro headed on target from a neat Sema cross, but the counter-attacking Blades had the last say of the half as Jebbison called Bachmann into action with a curling shot, and then skipper Egan steered a header towards goal.
The game continued in the same fiery vein after the break, with João Pedro becoming the fifth player to be booked by ref Smith for a challenge on Stevens before Egan was penalised for a tough challenge on the Brazilian.
But the Hornets retained their composure, and their efforts were soon rewarded. Kamara broke following a Sheffield United corner before the ball fell to Dennis who played in Sarr on the right, and the Senegal star squared to João Pedro who made no mistake from close range.