Reigning champions Saracens opened their Champions Cup defence with an eight-try thumping of Northampton Saints yet Mark McCall insists they cannot afford to let their momentum drop.

Saracens earned a 57-13 bonus point victory at Franklin’s Gardens, with Liam Williams scoring twice to put his side in control of Pool 2 after Clermont failed to earn a bonus point in their win over Ospreys.

In addition to Williams, Brad Barritt and Calum Clark also dotted down to ensure the bonus point was sealed before half-time.

After the break, Vincent Koch, Mako Vunipola, Alex Lozowski and Ben Spencer all got their names on the scoresheet, with Owen Farrell converting seven of the eight tries while also knocking over a penalty.

And as his side prepare to welcome Ospreys to Allianz Park next Saturday, director of rugby McCall couldn’t have been more impressed with his team’s relentlessness at both ends of the field.

“That was definitely our best performance of the year. And one of the really pleasing things was how long we sustained that for,” he said.

“The group challenged themselves at half-time to maintain the intensity we had in the first half. You could see the evidence of that.

“None of us thought it was going to end up the way it did. I think when we play like that and we win the collisions like we did then your attack is made a lot easier.

“It’s crucial that we can back up what we did. Ospreys pushed Clermont very close so it’s obviously huge for us next week.”