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 club-record European 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 Rugby and LV= Cup business for Leicester, with their European title ambitions ended prematurely.
Leicester, whose last Heineken Cup visit to Belfast in 2004 produced a 33-0 defeat – their previous tournament -worst, showed two changes from the side that saw off Aviva Premiership Rugby strugglers Wasps last weekend as props Marcos Ayerza and Martin Castrogiovanni both received call-ups.
Tigers, though, were without injured England trio Toby Flood, Manu Tuilagi and Louis Deacon, while Ulster received a double boost through their former Leicester fly-half Ian Humphreys and South African forward Pedrie Wannenburg being declared fit.
And the home side made a storming start, pinning Leicester on to the back foot through a succession of surges that severely tested Tigers' defence.
Wave after wave of attacking phases finally took a toll when Trimble crossed in the corner, although referee Romain Poite required television match official confirmation before awarding it. As if to remind Leicester about the size of their task, Pienaar booted the touchline conversion for a seven-point lead inside eight minutes, with Ulster enjoying complete control.
Leicester then threatened a breakaway through lively combined work by Alesana Tuilagi and Murphy, before Ulster regained a foothold and Pienaar kicked a penalty from just inside Tigers' half.
It was already proving a huge test of character for Leicester, but they responded in stylish fashion from first-phase possession when Twelvetrees made a half-break before Ben Youngs rifled out a defence-splitting pass to Murphy. Twelvetrees' successful conversion cut the deficit to three points, and Leicester grew in confidence, not only disrupting Ulster's impressive early rhythm but also looking dangerous when they shipped possession wide.
Pienaar, though, landed his second long-range penalty as the interval approached, and there was still time for Ulster to inflict a grievous blow on Tigers' hopes of a full-scale recovery.
Leicester wing Horacio Agulla was forced over his own line by some aggressive Ulster tackling, and the home side struck from quality scrum ball, with Trimble again benefiting. Pienaar narrowly failed with the conversion, yet Ulster were in control at 18-7 ahead halfway through a riveting encounter.
Twelvetrees missed an easy chance to put Leicester back in the contest when he hit the post with a penalty attempt from just 30 metres out, and Ulster then gained a foothold inside Tigers' half.
Pienaar showed Twelvetrees how it should be done 12 minutes later when he completed his penalty hat-trick, and Tigers entered the final quarter knowing their European ambitions were fading fast.
Another Pienaar penalty left Leicester trailing by 17 points as their discipline cracked under intense pressure, and Ulster now had designs on a try-scoring bonus point.
Pienaar's fifth penalty took the home side 20 points in front, before Leicester and England prop Dan Cole was yellow-carded for dissent to end a thoroughly miserable night for the Midlanders as Gilroy and Marshall struck the final blows.