Jason Day produced the highlight of the second round with an ace but the former world number one was unable to close the gap on fellow Australian Marc Leishman at the BMW Championship.
Day sent fans into a frenzy with a 189-yard tee shot at the par-three 17th that took a kick forward off the rough and eventually into the hole as the 2015 champion raised his hands in celebration.
However, Friday was all about Leishman who extended his lead to three strokes heading into the weekend of the third and final FedEx Cup play-off event.
Leishman - seventh in the rankings before the tournament got underway in Lake Forest, Illinois - dazzled on day one as he posted a 62 to set the early pace and the 33-year-old was at it again with another round in the 60s.
The two-time PGA Tour winner birdied eight holes and his only blemish came at the 17th as reached 16 under at the halfway stage.
As was the case following Thursday's first round, compatriot Day is Leishman's nearest challenge after his six-under-par 65, along with Rickie Fowler.
It was a mixed back for Day, who had two eagles and five birdies to go with his three bogeys at Conway Farms Golf Club.
American and FedEx Cup hopeful Fowler moved up the leaderboard thanks to his second-round 64, which featured six birdies and an eagle.
Next best is fellow American Patrick Cantlay, who carded a six-under-par 65 to be six shots off the pace, while Francesco Molinari (65) and Stewart Cink (66) are a stroke further back.
FedEx Cup leader and three-time major champion Jordan Spieth lost ground on Leishman after his 70.
Spieth was three shots behind at the start of play on Friday but the American star faltered, falling nine strokes back alongside the likes of Phil Mickelson (69) and Justin Rose (68).
Masters champion Sergio Garcia recorded back-to-back 68s, while US Open and Dell Technologies Championship winner Justin Thomas produced a 70 to be five under through 36 holes.
Reigning FedEx Cup champion Rory McIlroy showed signs of improvement with a 69 but the Northern Irishman remains well off the pace at one under.
It has been even worse for world number one Dustin Johnson, who finds himself languishing at the foot of the standings - one over to be exact.
Johnson won the first play-off event - the Northern Trust - but he has struggled this week, hitting a 72, having opened with a 71.