Spieth played the first two rounds alongside PGA Championship victor Justin Thomas and world number one Dustin Johnson - who came into the tournament second and third in the race for the $10mn playoff bonus that will be up for grabs at next week's Tour Championship.
Even now, with his game once again clicking and a smile back on his face, Jason Day sometimes shakes his head in disbelief when recalling the performance he authored at Conway Farms Golf Club two years ago. I don't tend to remember rounds of golf too often.
But Friday under sunny skies at Conway Farms, the toothy grin returned after a hole-in-one on No. 17, and Day's easygoing nature was back in full swing.
Day's 65 was remarkable given he hit just seven of 14 fairways and 11 of 18 greens in regulation, leading the former world No.1 to believe his best golf is yet to come with a hot putter.
"We were trying to land it 182 (yards) and I kind of pushed it".
Lahiri was done in by a disappointing finish over last three holes, where he bogeyed three times including two on the last holes in the second round.
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Fowler also finished strong, with three birdies and an eagle from the 13th through 17th of a 64 for 129.
The BMW Championship is the penultimate event of the FedEx Cup series and will determine the top-five seedings for next week's Tour Championship.
Jordan Spieth, No. 1 in the FedEx Cup after successive runner-up finishes in the playoff events, only managed a 70 and joined Mickelson in the group at 135. Northern Ireland's Rory McIlroy saw his slim hopes of defending the FedEx Cup playoff title dwindle further as his second-round 69 left him 15 off the lead.
The 28-year-old Northern Irishman captured the FedEx Cup title last year - and its $10 million bonus jackpot - but is now projected to finish 60th unless he makes a big move over the final two round, estimating he needed "a couple of 65s" to make any impact.
"Seeing the last two days, I know I still have it in myself to be able to hit the correct shots and go out there and try and win", Day said. "It isn't quite coming to together, it's about being patient".
McIlroy made five birdies, but carded a double bogey at the sixth and dropped another shot at the 13th.
On the seventh hole, Leishman chipped in beautifully before rolling the ball in on the long green for a birdie, before repeating the trick, putting in from beyond the fringe on the eighth.