The London club celebrated their overseas home debut in Brussels with a fine win that places them in control of Pool One after two rounds.
But the decision to empty the bench, taking off the brilliant Schalk Brits in the process, cost them momentum.
Tries from Chris Wyles - created by man of the match Brits - Steve Borthwick and Will Fraser fell one short of the four needed for the bonus point, but director of rugby McCall was unapologetic.
"Our philosophy at the club is that we have outstanding players on the bench and we'll use them. We'll continue to do that," he said.
"Schalk had an amazing first half and the question will be asked why he came off.
"But John Smit, who's no mean player himself, and Mako Vunipola came on and they've scrummaged a lot together.
"Racing's scrum was putting us under pressure and there are other areas to consider. Our scrum was very good in that last 20 minutes.
"We know there are downsides to the way we operate in terms of substitutions, but we believe they are outweighed by the massive upsides."
Saracens led 20-3 at half-time but Racing were able to gain a foothold after the interval until a late surge swept the 2011 Aviva Premiership champions clear.
Fly-half Charlie Hodgson was magnificent, finishing with 15 points as Saracens cemented first place in a formidable group that also includes Edinburgh and Munster.
"If you win 30-13 against a side like Racing, you have to be reasonably satisfied," McCall said.
"We went through every emotion today. There was some outstanding stuff in the first half, Racing were chasing shadows at times. But it was frustrating at times in the second half.
"Winning the match 4-0 in terms of points keeps us in control of the group. Nine points from the first two games is a pretty good return.
"The important thing is to gain control of your group and we've done that, but now we have the small matter of Munster back to back."
King Baudouin Stadium hosted an 18,202 crowd of which some 2,000 were Saracens fans who had made the trip across The Channel.
Taking the match to Belgium is part of Saracens' ambition to broaden their horizons, at least until construction of their new home at Allianz Park is completed in February.
"It was brilliant playing here. It felt like our first time at Wembley and the players were excited to come here," McCall said.
"It didn't feel like an away game because we had control of the ground.
"Everyone's enjoyed coming to Brussels. It was either play here or Watford..."
Wales prop Rhys Gill suffered rib cartilage damage and could be out for two to three weeks.
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