Dustin Johnson carded a course-record nine-under-par 63 to move into a tie for the lead at the BMW Championship.
The U.S. Open champion, who is third in the FedExCup points standings, finished a first round that was suspended due to storms with a five-under 67, two behind leader Roberto Castro.
But he is now level with Castro following a stunning performance on Friday at Crooked Stick Golf Club in Carmel, Indiana.
Johnson birdied two of the first three holes and made the turn at four under after holing out from the bunker at the ninth for an eagle.
Further gains at the 11th, 13th and 14th followed before Johnson recorded his second eagle of the day with a 31-foot putt at the 15th.
Castro - who carded his second straight 65 - came into the penultimate event on the FedExCup schedule in 53rd and is seeking to secure a spot in the top 30 and reach the Tour Championship.
The 31-year-old is enjoying the freedom of the format and not having a cut at this tournament, saying: "The whole play-offs, there's really only upside unless you start in the number-one spot, it's another week where there is a lot to be won."
Paul Casey is three strokes back in third on 11 under, one shot ahead of J.B. Holmes and Chris Kirk who are tied in fourth.
Holmes struck a 65 to boost his hopes of being one of the four captain's picks for the Ryder Cup, while Bubba Watson carded a five-under 67 to move into tied 10th as he aims to earn a spot on the United States team at Hazeltine later this month.
FedExCup leader Patrick Reed (70) and the second-placed Jason Day (67) are 10 strokes back, along with Rory McIlroy (72) and Jason Spieth (72).