Saracens started its quest for a third successive European Champions Cup with a 57-13 demolition of Northampton Saints, while Leigh Halfpenny's return to Toulon ended in an agonising defeat for Scarlets.

Sarries inflicted a 55-24 thrashing on Northampton on the first day of the Premiership season and the Saints were taught another brutal lesson by the defending champion in a Pool Two drubbing at Franklin's Gardens.

The Premiership leader had the bonus point in the bag before half-time and scored eight tries in a ruthless thrashing of the Saints, who lost Wales wing George North to a knee injury, in their own backyard.

Liam Williams finished off a slick move for the opening try on the left flank and added a second in the other corner either side of an unstoppable driving maul resulting in captain Brad Barritt dotting down, before former Saint Calum Clark scored a fourth try before the break.

The holder was 29-6 up at the break and showed no mercy after the interval, tries from Vincent Koch, Mako Vunipola, Alex Lozowski and Ben Spencer rubbing salt into the Saints wounds.

Owen Farrell scored 17 points from the tee on his return from a calf strain as the much talked about duel between England hookers Dylan Hartley and Jamie George become a mere sideshow.

Halfpenny threatened to return to haunt Toulon on his return to Stade Mayol, but the Top 14 side clung on for a 21-20 Pool Five win.

There was no sign of what was to come when the three-time European champions raced into an 18-0 lead midway through the first half following tries from Eric Escande and Guilhem Guirado.

Johnny McNicholl gave Scarlets hope with a try just after the break and Halfpenny darted through a gap to go over before taking his points tally for the afternoon to 15 with a second penalty to put his side in front.

Francois Trinh-Duc edged Toulon back into the lead with a penalty and Halfpenny, deemed surplus to requirements by Toulon after three seasons in France, missed a difficult kick to win it as Toulon edged the victory.

A Dan Evans double was unable to prevent Ospreys from suffering a 26-21 home loss to Clermont Auvergne in Pool Two, while Munster drew 17-17 in the Pool Four clash at Castres.