The 2011 champions earned themselves a bonus-point victory at Twickenham Stadium as they came through 42-20 winners.
"It was the start we wanted result-wise but I think the performance was patchy at points," McCall is quoted as saying on the league's official website.
"We were very good at times but other times I thought we were a bit ill-disciplined and let the game drift a little bit.
"But overall when we're in the right areas and when we're on the front foot we've got some big strong runners who can get us over the line."
Saracens play their first home match of the season next Saturday when they welcome Gloucester Rugby to the Allianz Park.