Ben Youngs nudged Leicester towards a Heineken Cup quarter-final place as his solo try stunned the Scarlets in an epic encounter.
Youngs' 40-metre dash for glory, which followed an Alesana Tuilagi touchdown 10 minutes earlier, means that a bonus-point victory over Welford Road visitors Treviso next Sunday should be enough to see Tigers progress as group winners or as one of two best runners-up.
If Perpignan beat the Scarlets and claim a five-point maximum in France, they will win Pool 5, but twice European champions Leicester can still expect to progress if they carry out a ruthless Italian job.
England outhalf Toby Flood kept the scoreboard ticking with five penalties and a conversion for 17 points at a windswept Parc-y-Scarlets, although the home side led 10-6 at half-time following wing Morgan Stoddart's try.
Stephen Jones added two penalties and a conversion, and Sean Lamont claimed an injury-time touchdown, but the Scarlets ultimately proved unable to avenge a 46-10 drubbing in Leicester three months ago.
Tigers substitute Steve Mafi finished the Scarlets off with a 79th-minute try, although Lamont had the final word, albeit an irrelevant one.
Leicester scored 26 points after the break, silencing the majority of a record 12,392 Scarlets' Heineken Cup crowd, proving that their status as clear English Premiership leaders is no fluke.
Flood's kicking, the finishing power of Youngs and Tuilagi, plus workaholic performances by flanker Thomas Waldrom and No 8 Jordan Crane, left the Welsh side's quarter-final hopes hanging by a thread.
They will need to beat Perpignan emphatically but the Scarlets will probably end up viewing last night's defeat as the game when their chances went west.
Leicester, though, remain firmly on course for a 10th quarter-final appearance, leaving the Scarlets to reflect on a case of what might have been.
In the other encounter in Pool 5, Perpignan kept themselves right in the chase for a quarter-final spot with a 44-9 bonus-point victory against Treviso at Stadio Comunale di Monigo, with Gregory le Corvec, Farid Sid, Nicolas Laharrague and Julien Candelon (two) all crossing the whitewash to seal a comfortable win.
Sunday Indo Sport