In Saracens first match since their relegation from the Premiership Ealing took the win 27-26.
Only Vanipola was in action for Saracens for the Trailfinders Challenge Cup opener.
He had a quite game and did not make an impression on Ealing. Making their first outing since being relegated last season as punishment for repeated salary cap breaches, McCall’s men were also missing eight players suspended for breaking coronavirus rules when on Barbarians duty.
First over the line was Angus Kernohan over but the try was made possible by a dummy from scrum-half Craig Hampson that deceived a visiting defence that was pinned close to their line.
Otherwise all the points in a tight opening quarter were supplied by penalties from fly-halves Craig Willis and Will Hooley.
Vunipola became increasingly involved as the half progressed, carrying into heavy traffic and barrelling into the breakdown, but Saracens met with stiff resistance from fired-up opponents.
As half-time approached, their big ball-carrying forwards began to make an impact and it was the steam-roller approach that created field position for their first breakthrough.
A solid five-metre scrum saw Vunipola pop a pass to Aled Davies and the speed of the play outwitted Ealing as full-back Elliot Obatoyinbo dived over.
Trailfinders finished the half with a flourish and went close early in the second before sustaining pressure on the visiting line by winning a Saracens scrum and then battering away.
The assault ended when hooker Alun Walker forced his way over, but the score only served to ignite McCall’s men and they began attacking with greater purpose until replacement front-row Kapeli Pifeleti finished a line-out maul.
But the game tilted on its axis again when Walker grabbed his second with Willis converting to put Ealing beyond reach.
Saracens hooker Tom Woolstencroft finished a forward assault from a short-range free-kick, but the match had already entered stoppage time.