The 19-year-old Italian had four birdies in a row when third-round play resumed Sunday morning and two more on the back nine to reach 11-under 202 overall.
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South African Louis Oosthuizen shot a 65 to move into second place at 9 under, one stroke ahead of England's
Organizers of the $6 million event were forced to complete most of the second round on Saturday due to heavy rains the first two days of the tournament, pushing the start of the third round back to the late afternoon.
Golfers were back on the course to start the final round Sunday immediately after finishing the third.
Overnight leader Thomas Bjorn of Denmark slumped back to a share of fifth place at 6 under after hitting five bogeys to card a 74 in the third round
Rory McIlroy also couldn't make up any ground on the leaders, shooting a 69 to move to 4 under overall, seven strokes back.