That score, along with Ryan Lamb's conversion and earlier penalty, put the visitors within three points of the hosts, but his yellow card for a tackle on Farrell allowed Sarries to get on top.
Ashton crossed to establish an 18-10 lead at the break after a delay to see if there had been a forward pass in the build up, and Sarries cruised to victory in a one-sided second period.
Vunipola bundled over for the home side's third try soon after the restart as they made full use of their man advantage.
Tigers responded and, with their wind at their backs, they started to boss territory.
But, despite Farrell's exit, Sarries secured a bonus-point when a brilliant run by replacement Neil de Kock saw him dance through the Tigers defence and find Wray who went over from close in.
Vunipola was then instrumental in forcing a penalty try and Sarries completed a miserable afternoon for Tigers when de Kock found Ashton with a clever inside pass and the England wing went over in the corner.
Farrell's replacement, Charlie Hodgson, added his third conversion to add to the 13 points Farrell had kicked to round off a fine afternoon for the home side.
Ransom for Goode (69), Hodgson for Farrell (66), de Kock for Wigglesworth (53), M. Vunipola for Barrington (41), Johnston for Stevens (53), Kruis for Hargreaves (56), Wray for Joubert (66).
Hepetema for Smith (41), Mele for B. Youngs (65), Ayerza for Stankovich (45), Schuster for Briggs (45), T. Youngs for Balmain (45), De Chaves for Kitchener (74), Waldrom for Matera (53), Thompstone for Hepetema (46).
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