Saracens claimed top spot in Pool 3 with a bonus-point victory over Zebre.
George Kruis, Ernst Joubert and Chris Wyles all crossed before Chris Ashton scored twice in the space of eight minutes to wrap up the victory.
Samu Vunisa claimed a late consolation score for Zebre but it was never enough to trouble the
visitors who recovered from their defeat to Toulouse at Wembley Stadium to get their campaign back on track.
McCall said: "It was a really good performance because we did a very clinical job on Zebre, especially in the first half. The energy of the group in the opening 35 minutes was outstanding, we took our chances when they were there.
"We made heavy weather getting the bonus point but you have to give credit to Zebre because they came out in the second half and fought really hard. So I'm delighted to have come away with the bonus-point win."
From the moment Charlie Hodgson kicked Saracens ahead from the sixth minute and they rarely looked likely to surrender the lead.
Zebre were made to pay for errors as the power of the Saracens pack proved decisive.
Second-row Kruis crashed over from five metres out on 13 minutes, converted by Hodgson who added a penalty before another set-piece move saw Saracens claim their second try.
Number eight Joubert stormed over from a well-worked lineout and despite Hodgson missing the conversion from out wide, Saracens led 18-0 after 24 minutes.
Alex Goode made the most of Samu Vunisa's yellow card with a counter-attack that saw Ashton hand Wyles a simple finish in the corner.
Zebre were reduced to 13 men when Mauro Bergamasco joined Vunisa in the sin bin though Gonzalo Garcia kicked the first points of the second half.
Ashton then scored twice in the space of eight minutes following good work by first Hodgson and then Goode however, Zebre finished the stronger when Vunisa scored following a yellow card for Saracens replacement Duncan Taylor.
McCall added: "What pleased me most this week was how good our preparation and mentality was.
"We actually gave them a lot of respect in the build up to today's game, and we knew how difficult today could have been.
"Monday, Tuesday and Thursday training was at a very high level and I suppose we have to do the same this week and make sure we have the correct attitude which I'm sure this group will."