Brooks Koepka was gifted the halfway lead at the FedEx St Jude Classic after Steven Alker's shocking finish to the second round in Memphis.
Koepka, winner in Phoenix earlier this year, will go into the weekend with a one-shot lead after adding a solid 67 to his opening 64, while Alker dropped three shots over the final two holes to slip two shots off the pace.
Koepka cruised to the turn one under for the day and picked up birdies at 15 and 16 before parring in to claim the outright lead on nine under, but he was soon overtaken when Alker carded four birdies in seven holes.
But the Australian missed a six-footer for par at the short eighth - his 17th - and he then hacked his way from rough to rough at the ninth, taking four shots to reach the green before two-putting for a scrappy double-bogey six.
Koepka's closest challenger heading into the third round is Austin Cook, who started on the 10th and enjoyed a run of five birdies in six holes from the 11th before further gains at five and nine capped an excellent 64.
Alker is alone in third, while Scotland's Russell Knox is a further stroke behind after he returned a flawless six-birdie 64 to move to six under alongside first round joint-leader Greg Owen.
The English journeyman followed his opening 64 with one birdie, one bogey and 16 pars in an uneventful 70, but his compatriot Brian Davis slipped to three under after an erratic 72.
Phil Mickelson also failed to make much happen as he posted a two-birdie, one-bogey 69 to move to three under with Luke Donald, who was similarly consistent in his 68.
But Graeme McDowell's hopes of a confidence-boosting week ahead of the US Open were scuppered as he added a 73 to his first-round 76 to finish well down the field on nine over par, while his Ryder Cup team-mate Jamie Donaldson (+10) also missed the cut by a distance.