Bullard, sidelined since early October with knee ligament damage, was introduced in the second half with his side leading 2-0 thanks to a first-half double from striker Jay Simpson.
Ched Evans then scored twice as the Blades, booed off by sections of their home support at half-time, staged a brave second-half fightback.
Simpson, who ended his season-long goal drought last week with both goals in Hull's 2-0 home win over Bristol City, opened the scoring in the third minute and converted a penalty in first-half stoppage time.
Evans pulled one back for United in the 62nd minute and fired an equaliser 11 minutes later, but Bullard, in only his fifth appearance of the season, converted another cross from on-loan Manchester United midfielder Cameron Stewart, who also set up both Simpson's goals, in the 93rd minute.
United caretaker-manager John Carver named the same side that started in the 1-0 win over Swansea in his first game in charge last Saturday.
Kevin Kilbane was recalled at left-back for Hull in place of the suspended Andy Dawson.
Simpson gave Hull a flying start when he clinically despatched Stewart's fine cutback from 12 yards in the third minute after a flowing move down the right involving Robert Koren and Liam Rosenior.
The Blades were dealt another early blow when defender Andy Taylor was forced off with what looked like a serious injury and replaced by Matt Lowton in the 12th minute.
Hull winger Jamie Devitt clipped a free-kick over the crossbar soon after, following Evans' high tackle on Kilbane, which led to the visiting defender hobbling off several minutes later due to a gashed head. Fellow Irishman Paul McShane was sent on in his place.
The Blades were forced into another change late in the first period when injured midfielder Stephen Quinn was replaced by Jamie Ward.
Neither side created a clear goalscoring chance after Simpson's opener until Hull doubled their lead deep in time added on at the end of the first half.
Blades centre-half Nyron Nosworthy tripped the impressive Simpson in the area and the former Arsenal striker picked himself up and confidently sent home goalkeeper Steve Simonsen the wrong way with the subsequent penalty.
Lowton's header from Andy Reid's corner six minutes into the second half prompted Hull goalkeeper Vito Mannone into his first meaningful save and Blades winger Mark Yeates fired over the crossbar soon after.
Bullard replaced Koren in the 62nd minute, but the Blades cut the deficit moments later when Evans lashed the ball into the bottom corner following Reid's ball into the box.
Reid set Evans up for his second and the Blades' equaliser nine minutes later. The Irish midfielder, on loan from Sunderland, crossed again from the right and the Wales international finished in similar fashion from inside the area.
But United were dealt a late knockout blow when Bullard swept home Stewart's cross in the third minute of time added on to extend the Tigers' unbeaten run to seven matches.