Sarries made light of the snowy conditions that threatened to blight their last-ever game at Vicarage Road, scoring five tries to qualify from the pool stage for the second season in a row.
Five minutes later Farrell, playing at outside centre, doubled his side's advantage with a long-range penalty after Robin Hislop had lost his bind at a scrum.
As expected, Sarries were having the majority of possession and Farrell soon had another three points to add to his tally after Dougie Fife held on to the ball in the tackle in his own half.
The hosts' first try arrived in the 27th minute when Richard Wigglesworth chipped the ball towards the right-hand corner and Ashton was left all alone to touch down.
Farrell's conversion from out wide came back off the near post - bringing to an end a run of 26 successful kicks.
Almost out of nothing, Edinburgh hit back when full-back Greig Tonks booted the ball downfield and chased ahead.
His opposite number Wyles fumbled, allowing Tonks to pick up and score with Greig Laidlaw's conversion bringing the deficit down to seven points.
The try really energised the visitors for the rest of the half, but they were unable to make any more progress before the break.
Farrell then had the chance to extend his side's lead early in the second half but could only push a kickable penalty wide.
But his vision a few minutes later led to Ashton's second try when he quickly smashed a penalty towards the right wing, where the England flyer was waiting to gather and run in.
The bonus point moved within sight with 27 minutes still to play when an attacking line-out following a penalty drove its way over the tryline with former England prop Stevens touching down.
Farrell got himself back on track by adding the extras but Sarries were unable to immediately pile on the pressure as play began to get scrappy.
David Strettle thought he was going to be the man to get that fourth try when he chased down Hodgson's grubber but was judged to be offside.
The home side were left frustrated again when another Hodgson kick was gathered by Brad Barritt, only for him to be superbly held up by Fife.
With five minutes left, Hodgson sealed the bonus point himself when he checked inside before going through a gap, prompting wild celebrations amongst the Saracens players.
There was still time for one more try at the death when another Hodgson kick ahead was just missed by Joel Tomkins, but Wyles was there to follow up.