Full-back Jack Smith was the hero and villain after Neil Warnock's promotion favourites grabbed a late equaliser against ten-man Watford.
The 20-year-old defender had scored in the 64th minute after keeper Lenny Pidgeley had been sent off, striker Heidar Helguson adding a second before United were handed a lifeline as Jack Lester scored from the spot after Smith handled.
United, who had struggled to find their rhythm, against a hard-working Watford side, broke clear in the 20th minute, Michael Tonge picking out Nick Montgomery but the Blades midfielder, under pressure from Marcus Gayle, fire wide of the target from 16 yards.
Michael Brown, recalled to the side before the start of a four-match suspension, pulled a free kick over the top before the Sheffield side were caught on the break again, Paulo Vernazza drilling in a half-volley but the Watford midfielder miscued and Alan Fettis tidied up.
The United keeper, on loan from Hull, foiled Watford seconds before the interval, beating Helguson to Paul Devlin's centre to punch clear before pouncing again to foil Scott Fitzgerald in a chase for the ball.
Centre back Phil Jagielka broke the deadlock in the 52nd minute, rising at the far post to meet Tonge's corner to head past Pidgeley from close range.
Watford were in deeper trouble in the 58th minute when Pidgeley was sent off as he darted from his area and handled as Lester burst through, 39-year-old Alec Chamberlain taking over in goal.
The Vicarage Road side were back on level terms in the 64th minute - Devlin prodding the ball to Smith whose angled drive flashed past Fettis and into the far corner.
Helguson added the second three minutes later stretching at the far post to meet Neal Ardley's cross from the left flank.
The veteran Watford keeper served up a couple of stunning saves as United looked for the equaliser. He blocked substitute striker Ashley Ward's effort and then kept out Lester before Smith suffered a rush of blood to the head in the 84th minute sticking out a hand to divert a Stuart McCall centre.