Leishman finished third two weeks ago at the TPC Boston and moved to No. 7 in the FedEx Cup.
Carding a seven-under 64 in the second round, the American shot three birdies before the turn on Friday, followed by another three on the back nine, impressing the spectators with an eagle on the par-5 15th hole.
The 33-year-old regained the stroke with a flawless 20-foot putt at the fifth, although he then missed from four feet for par at the seventh before a nice up-and-down at the par-five next got him back under the card for the day.
"The 62 was obviously pretty nice, but today was nearly as satisfying going into a Saturday with a lead to play the way I did", Leishman said.
'The game's feeling really good. It's very easy to have bogeys out there.
The BMW Championship is the penultimate event of the PGA Tour season. Should Leishman go on to win the BMW Championship, he would join five players who have won this this event in wire-towire (no ties) fashion.
Zidane told me apart from Messi, I'm the best left footer - Asensio
The 21-year-old has made an impressive start to the season and Zidane has clearly been impressed to laud his performances.
The 29-year-old came back from three bogeys to put in another spectacular performance with an eagle on the 14th, ending round two with a six-under 65. In 36 holes played, he has made a remarkable 18 birdies, his relentless pace stringing out the field in behind.
Marc Leishman is leading the BMW Championship midway through the final round.
For the first two rounds of his new relationship with caddie Luke Reardon, Jason Day raced up the leaderboard at the BMW Championship. "I need to make the Tour Championship - that's my ultimate goal".
Smith, who bagged a first PGA Tour win at the Zurich Classic in April, gave himself a red-hot chance at making the finale of the $US67 million play-offs series with a three-under-par 68 during Friday's second round elevating him to eight-under sharing seventh.
Fellow Australian Day (5/1), Charley Hoffman (16/1) and Jamie Lovemark (25/1) were his nearest challengers on seven under, while Fowler (7/1) lies in the group a further shot back after birdieing six of his final seven holes.
Defending champion Dustin Johnson struggled again and was 16 shots behind.
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