Scarlets, who have beaten Aviron Bayonnais (39-7) and Toyota Cheetahs (45-26) so far in the EPCR Challenge Cup, came into the game in Llanelli with just one URC win to their name this season.

Dragons, who are sixth in EPCR Challenge Cup Pool B, led 17-16 at the break thanks to tries from Angus O'Brien and Lewis Jones.

And with Scarlets’ Kalamafoni dismissed for punching, the visitors looked well positioned to claim victory.

But the hosts, who had dotted down through Steff Evans in the first half, bossed proceedings following the restart, crossing through Dane Blacker and Johnny McNicholl while Halfpenny’s boot aided their cause.

Two other EPCR Challenge Cup sides fell to away defeats in the URC on Sunday, with Cardiff Rugby going down 22-19 at Ospreys and Connacht Rugby beaten 41-12 at Leinster Rugby.

Owen Lane, Liam Belcher and Josh Adams notched tries for Cardiff, who are top of EPCR Challenge Cup Pool A, but Jarrod Evans was narrowly short of kicking a late penalty to snatch a draw.

Connacht, fourth in EPCR Challenge Cup Pool A, were well beaten in Dublin, though David Hawkshaw and Tom Farrell crossed for consolation scores.

Full-back Leigh Halfpenny kicked 18 points as EPCR Challenge Cup Pool B leaders Scarlets beat Dragons 33-17 in the United Rugby Championship (URC) on Sunday, despite seeing Sione Kalamafoni sent off in the first half.