Paul Casey one off midway lead at Deutsche Bank Championship

Kevin Chappell holds a one-shot lead over Paul Casey and Jimmy Walker after the second round of the Deutsche Bank Championship.

Chappell posted a seven-under 64 on a day of low scoring at TPC Boston, while Casey posted a bogey-free 66 to join Walker on 10 under at the halfway stage.

Dustin Johnson looked set to threaten for a share of the lead until a double-bogey for the last, while Rory McIlroy sits seven strokes off the pace after a much-improved putting display.

Smylie Kaufman took the early lead after playing the first seven holes in seven under, mixing five birdies with an eagle, only to slip back by bogeying his next two holes.

The American was replaced by Brian Harman at the top of the leaderboard when he followed a back-nine 31 with three more gains after the turn.

Despite missing an eight-footer and posting a final-hole bogey, Harman's six-under 65 set the clubhouse target at nine under.

Chappell took a share of the advantage when he holed out from the seventh fairway for eagle, before moving out ahead with a birdie-two at the next.

A misjudged chip saw Chappell drop a shot at the 13th and slip back to nine under, with Casey moving in to a three-way tie soon after three birdies in a four-hole stretch from the third.

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Back-to-back birdies from the 15th saw Chappell reclaim top spot at 11 under, as Casey rolled in from 10 feet at the seventh and finished in regulation to sign for a five-under 66.

Four gains in a seven-hole stretch along the back nine briefly lifted Johnson within one of the lead, only for the US Open champion to go out of bounds on his way to a seven at the par-five 18th.

Walker sunk a 25-foot eagle at the seventh and added a gain at the ninth to match Chappell's 64, while Johnson sits joint-fifth at eight under with Kaufman.

A final-hole birdie lifted Jordan Spieth in to the group alongside Sergio Garcia on six under, with Adam Scott and Zach Johnson joining McIlroy a further two strokes back.

Day recovered from a quadruple-bogey eight at the fifth to card three birdies over the back nine and avoid an early exit, but Phil Mickelson and Graeme McDowell were among those to miss the cut.

Watch the Deutsche Bank Championship throughout the weekend live on Sky Sports 4 - your home of golf. Live coverage of the third round begins on Sunday from 6pm.