Tiger Woods put himself well on track for an eighth Bridgestone Invitational title with a stunning course record 61 that left him seven shots clear of Keegan Bradley, his nearest rival.
His second-round total at Firestone equalled his lowest ever round in his professional career and consisted of seven birdies and an eagle.
Woods holed from three feet for a birdie at the first and 20ft for eagle at the second then got up and down for par on the next two holes – the latter from a greenside bunker – and then made a more adventurous par on the sixth after his pulled drive ended up at the base of a tree.
From there he could only chip out across the fairway alongside playing partner Hideki Matsuyama's tee shot, but after hitting his third shot into 25ft the 14-time major winner holed for an unlikely four.
A superb tee shot to within three feet of the pin on the seventh set up another birdie from the seventh one-putt of the round, but that run finally came to an end with a two-putt par on the eighth.
A birdie putt from 15ft on the ninth narrowly missed but Woods was still out in 30 and, at nine under, three shots clear of Bradley and Simpson.
Woods was not about to slow down either, holing from seven feet on the 10th, five feet on the 11th and 20ft on the 12th for a hat-trick of birdies to leave the field trailing in his wake.
The 37-year-old was now six shots clear and eight under for the round, needing to play the last six holes in three under to shoot a magical 59 for the first time in his career.
Woods made the most of a stroke of good luck on the 13th, hitting his approach to 15ft and making the birdie putt after his drive had bounced off a tree and back into the fairway.
Another bad drive on the next was not so fortunate, although Woods did have a shot through the trees and was able to find the back of the green, from where he chipped to six feet and holed for par.
Almost unnoticed in all the excitement, Bristol's Chris Wood, helped by birdies on 15 and 16 finished level with Bradley to earn a share of second spot, seven behind Woods.
Woods has been drawn to play alongside former champions Bradley and Davis Love III in the first two rounds of next week's US PGA Championship at Oak Hill.