Mahan’s eight birdies were enough to seize the lead from early second-round pace-setter Merrick, who equalled the Glen Abbey course record with a 10-under 62 that included an eagle and eight birdies.
Mahan had a 13-under total of 131, with Merrick on 11-under 133. Former Masters champion Bubba Watson was alone in third place after a 67 for 135, and it was a further stroke back to Patrick Reed (68) and Australian Aaron Baddeley (68) on 136.
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