Leicester are facing an early exit for only the fifth time in 15 Heineken Cup campaigns after they were battered into submission and suffered a 41-7 defeat at Ravenhill.
The Tigers now cannot win Pool Four - which offers an automatic quarter-final place - after Ulster moved six points above them ahead of next weekend's probable group decider against French heavyweights Clermont Auvergne.
Tigers will need a bonus point victory over Italian strugglers Aironi at Welford Road to give themselves any chance in the race for two best runners-up spots, yet teams in other pools appear better placed.
Leicester were undone by two first-half tries from Ireland international wing Andrew Trimble, while Ulster's South African scrum-half Ruan Pienaar put the boot in with five penalties and three conversions for a 21-point haul before wing Craig Gilroy and replacement Paul Marshall added late tries.
Skipper Geordan Murphy claimed an early touchdown for the Tigers, converted by fly-half Billy Twelvetrees, but Leicester did not score after the 16th minute as Ulster dominated.
A capacity 11,700 crowd roared its approval for a Herculean effort by the home side, who had heroes everywhere, notably Pienaar, hooker Rory Best and captain Johann Muller.
Leicester, in contrast, could never establish sufficient momentum to threaten a rare Heineken Cup home defeat for Ulster, and there appears every chance of three Irish teams reaching the last eight, given that Munster and Leinster lead their groups by considerable margins.
Unless they benefit from a series of unlikely results next weekend, it will be back to Aviva Premiership and LV= Cup business for Leicester, with their European title ambitions ended prematurely.