Leishman, who goes into the weekend with a three-shot lead over Day and Fowler, told the PGA website: 'The game's feeling really good.
Day, who last won 16 months ago, chipped in from behind the 14th green for his second eagle of the week, and then added a third eagle with one swing, which was actually a hole-in-one on the Par-3 17th hole with a 7-iron that turned into a payoff for multiple parties. "So the combination of those two things on a PGA Tour course is not a very good one", Leishman said. "It was a lucky hole-in-one, I guess", Day said after his second ace on tour.
"It was a lucky hole-in-one, I guess".
"Last week showed that leading by a couple of shots going into the back nine is not enough and there is a lot of great players just behind me so I need to keep the foot on the pedal".
To hear him talk of his wire-to-wire victory at the 2015 BMW Championship that took him to No. 1 in the world is to listen to someone describing an out-of-body experience.
"I don't know if I'll ever get back there", Day said.
The generous Day then donated the BMW M760i he won for the ace to the Evans Scholar foundation which provides college scholarships to caddies.
Fowler also finished strong, with three birdies and an eagle from the 13th through 17th of a 64 for 129.
He already has 18 birdies in 36 holes at Conway Farms, where the scoring average was a shade under 69 through two rounds.
It hasn't been easy for defending champion Dustin Johnson, who is facing putting problems.
Patrick Cantlay extended his remarkable run this season with a 65, leaving him alone in fourth place but six shots behind.
The Northern Irishman needs a top-four finish to reach the Tour Championship, the final Tour event of the season.
Leishman came into the BMW Championship ranked seventh in the FedEx Cup standings after finishing third at the Dell Technologies Championship.
The BMW Championship is the penultimate event of the PGA Tour's $US67 million FedEx Cup series and will determine the all-important top-five seedings for next week's Tour Championship in Atlanta.