With the match about to go into injury-time it was on-loan Wasps prop Kershaw who went over from close range to win the match, Andy Goode adding his 16th point with the boot to finish the scoring in a match which saw four tries apiece.
Harlequins fielded a team including Ireland hooker Keith Wood, who missed his side’s win over Australia the day before with a neck injury – the Ireland management happy for the Lions star to turn out for his club.
Not so happy were the Fiji Rugby Union, who had been deprived of star centre Viliame Satala ahead of Saturday’s heavy Test loss to Wales, Quins refusing to release him due to Fiji’s paperwork arriving late.
Despite having their two internationals on the field, two tries from wing Matt Moore and one each for South African import André Vos and scrum-half Nick Duncombe were not enough in the end.
Saracens had shot out of the blocks with early tries from Australian centre Tim Horan and discarded England scrum-half Kyran Bracken, while England Sevens star Richard Haughton grabbed their third before the break.
But it was Kershaw’s score at the death that brought the Vicarage Road crowd to its feet, as Sarries recorded a morale-boosting win in the London derby.
For Saracens:Tries: Horan, Bracken, Haughton, KershawCons: Goode 2Pens: Goode 4
For Harlequins: Tries: Moore 2, Vos, DuncombeCons: Williams 2Pens: Williams 2