American Jimmy Walker has taken the lead at the halfway stage of the Wyndham Championship.

Walker shot a bogey-free round of 62 to hold a one-shot advantage over Webb Simpson, who hit seven birdies on the way to a round of 63.

Spain's Sergio Garcia lies a shot further adrift as he attempts to qualify for the Fedex Cup playoffs and make a late bid to earn a place in Europe's Ryder Cup team.

First-round leader Carl Petterson carded a two-under-par 68 to finish level with Garcia, while Welshman Jamie Donaldson leads the British challenge on six-under.