Centre Paul Asquith scored a try in the final minute as Scarlets pulled off a remarkable 33-28 Champions Cup bonus-point victory over Benetton at Parc y Scarlets.
It looked set to be a comfortable home victory when Scarlets went 14-0 up after six minutes and then Benetton had flanker Francesco Minto sent off for a dangerous tackle in the 24th.
But after 70 minutes the visitors, who had been 21-7 down, found themselves 28-21 up with a bonus point and all set to celebrate their first win in Europe for more nearly three years.
Scarlets' nerves held firm however to set up a grandstand finish and score two tries in the final four minutes to claim their first win in Pool Five.
Scarlets' try scorers were scrum-half Gareth Davies (two), Tadgh Beirne and Steff Evans with Leigh Halfpenny kicking three conversions and Rhys Patchell one. Benetton's tries came from number eight Robert Barbieri, full-back Jayden Hayward, wing Angelo Esposito and lock Federico, with fly-half Tommaso Allen kicking four conversions.
Scarlets went into the game heavily loaded with talent having recalled 10 internationals. The Welsh outfit seemed well on the way to victory as early as the sixth minute with Gareth Davies going over for two tries as the Italians were caught cold twice by the livewire scum-half.
The first came in the second minute with Davies racing in after lock Beirne won line-out ball just inside the 22 before the scrum-half was over again after good build up work by Patchell and James Davies. Halfpenny converted both tries.
Benetton got on the scoreboard in the 14th minute after a concerted attack saw Barbieri dive over from short range. Allan converted to half Scarlets' lead.
The visitors went in search of a second and went close but Asquith intercepted and although the ball got back to Patchell, he was put into touch on halfway.
The match took a significant turn in the 24th minute when Minto upended David Bulbring with the Scarlets lock landing on the back of his neck.
After calling in the TMO and seeing half a dozen replays on the big screen, referee Mathieu Raynal sent off the flanker.
Two minutes later Scarlets were over for their third try with Beirne emerging from a pile of bodies in the left corner, Halfpenny kicking his third conversion.
Patchell missed touch with a penalty and the Scarlets paid the price as 14-man Benetton counter-attacked and scored their second try through Hayward, converted by Allan.
Scarlets went into half-time 21-14 up but was the Italian side that scored first after the break with wing Esposito going over in the right corner with Allan's conversion levelling the scores at 21-21 in the 56th minute.
Matters got worse for the home team when James Davies received a yellow card for persistent offending at the ruck just after the hour mark.
Constant pressure from Treviso finally got them their reward with a bonus point try for Ruzza. Allan converted for a fourth time as the visitors led 28-21.
But Scarlets pulled off a dramatic finale with two tries in the final four minutes to steal the win. First Evans went over for a try converted by Patchell. Evans then put through a kick which Asquith collected and scored. Patchell missed the conversion but Scarlets celebrated their first win in the pool.
