Oosthuizen drained seven straight birdies early in the round, raising the possibility of a 59 at TPC Boston. The streak came to an end on the 10th hole, however, and the South African played at a par pace the rest of the day.
The stellar round was good for a 54-hole record at the second event of the PGA Tour Playoffs -- a 19-under 194.
That put Oosthuizen three shots ahead of second-round leader and world No. 1 Rory McIlroy, who carded a 4-under 67 and ended the day in second place at minus-16.
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