Grace shot a 5-under-par 67 Friday at the St. Andrews Old Course. That, combined with his European Tour-record-tying 12-under 60 at Kingsbarns Thursday, has him at 17-under 127 after 36 holes.
He is to play Carnoustie Saturday. Players rotate among those three courses in the first three rounds.
Thorbjorn Olesen turned in a 3-under 69 at Carnoustie while Joel Sjoholm matched Grace's 67 at St. Andrews, leaving them tied for second at 12-under 132. Anton Haig, who shot 68 at St. Andrews Friday, is in fourth at 11-under.
Grace opened his Friday round with three pars but had his first bogey of the tournament at No. 4. He immediately got that stroke back with a birdie at 5 and protected his lead with four consecutive birdies over Nos. 7-10. A birdie at 18 made the lead five strokes.
Swim Week Miami Beach 2014 [PHOTOS]