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No less than 83,889 people turned out to watch Sarries record a 39-17 win, with Farrell standing out thanks to his personal tally of 17 points that featured a try, three conversions and two penalties.
And McCall believes for his age that Farrell is certainly proving to be a mature head on the field thanks largely to his experiences on the international scene.
"We rotate our squad regularly throughout the season so Owen Farrell's game time is exactly where it should be so there was no necessity to rest him," said McCall.
"You can see how much Farrell has improved since last summer. The Lions tour has made a huge difference to him. He's such a mature 22-year-old.
"I would've taken a 39-17 victory over Harlequins at Wembley before the game though. We've come through unscathed injury-wise.
"We played some outstanding rugby at times, our intent to play was really good today but it's just a little bit frustrating that we handed them some field position and momentum through ill-discipline."