Saracens director of rugby Mark McCall has claimed that Billy Vunipola's yellow card was the spark for a "strong, resilient team performance" at Ulster.

The Aviva Premiership leaders came back from nine points down to beat the Irish province and move to the top of their European Rugby Champions Cup pool.

McCall told reporters: "We had to work really hard for it. The first 20 minutes we hadn't done all that wrong but we were 9-0 down and I think that's what that team has. They are very experienced and very resilient and found a way to claw their way back into the game in the second 20 minutes of the first half.

"At half time, 9-5 was okay for us and we'd chosen to play into the strong breeze but then when we didn't capitalise on the pressure we had built early in the second half we were a little bit worried when Billy got sin-binned.

"But I thought we were magnificent in that 15-minute period. Our half-backs were superb, they probed the corners and ran at the right times."

The pool's other sides, Toulouse and Oyonnax, face each other later on Saturday.