Matt Kuchar drives clear at the BMW
The American Ryder Cup newcomer, now in with a great chance of the 6.5million jackpot in a fortnight's time, had an eagle and six birdies to be one ahead of compatriot Ryan Moore.
England's Luke Donald and Justin Rose, meanwhile, set off with 68s and shared fourth place midway through the day's play.
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Hide AdKuchar started the four-tournament series by beating Scot Martin Laird in a play-off for The Barclays title in New Jersey and maintained top spot with a 11th place finish at the Deutsche Bank Championship in Boston on Monday.
Donald, joint second on Monday five strokes behind American Charley Hoffman, and Rose both had six birdies and three bogeys, while Hoffman had to be content with a 70 and Laird managed only a two over 73, the same as Brian Davis. "Three bogeys was a little disappointing just because I didn't short game it well enough," said Donald.