Ryan Palmer held on to a share of the lead at the Deutsche Bank Championship after shooting a level par 71 at TPC Boston on Saturday.
Palmer is joined at the top by Australian Jason Day, who carded a three-under-par 68 in his second round.
Ian Poulter, who is hoping to earn one of Paul McGinley's wildcard spots for next month's Ryder Cup, failed to build on his promising opening round as he posted a 73.
The best-placed European golfers are Scotland's Russell Knox and Martin Kaymer, who showed good form to card a 66 and reach the halfway mark on five-under-par.
Another Ryder Cup wildcard hopeful, Luke Donald, endured a disappointing day as he slipped down the field in Massachusetts with a second round of 74.
