The birdie put MacKenzie at 20-under 268, one shot shy of a tournament record and a stroke better than Bob Estes.
Only three of the previous seven champions will be in the field this week, including MacKenzie. Some of them -- like two-time winner Vaughn Taylor and Scott Verplank -- will be playing at the Bridgestone Invitational.
Tadd Fujikawa will also be on hand, playing as a professional. Fujikawa, you might recall, became the second-youngest player to make a PGA TOUR cut at the Sony Open in January.
It came just four days after his 16th birthday.
GOLF CHANNEL will have exclusive coverage of all four rounds, beginning at 6:30 p.m. ET on Thursday and Friday and at 9:00 p.m. ET on both weekend days. It will air replays of every round early in the morning.