Chris Kirk was the surprise halfway leader and Padraig Harrington moved into contention but defending champion Anthony Kim stole the show in the second round of the Shell Houston Open.
Kirk added a round of 69 to his opening 66 to improve to nine-under-par, while Harrington also scored 69 to reach seven under. However Kim, after an opening level-par round, signed for an eight-under 64 to hurtle up the leaderboard and reach a tie for second place with Johnson Wagner, who carded 67.
Irishman Harrington, a three-time major champion, had looked set to move into a handy lead at the top of the leaderboard as, starting from the 10th, he recorded birdies at the 11th, 12th, 15th, 16th and 17th.
Harrington's only dropped shot on his opening nine holes had been at the 14th, but his round took a turn for the worse as he ran up a hat-trick of bogeys from the second to drop back to just one under on the day. However, an eagle at the par-five eighth allowed him to claim a share of fourth place.
Twenty-five-year-old American Kim spent much of his round having to recover from inaccurate tee shots, conjuring two superb shots from fairway bunkers to record birdies.
The 2008 Ryder Cup star ended up with eight birdies and remarkably no dropped shots.
Kirk had a double-bogey seven on hole four - his 13th after starting on the back nine - but finished birdie-birdie to seize the lead.
The 25-year-old former University of Georgia student had his first PGA Tour top-10 finish at January's Bob Hope Open but his game had recently gone off the boil, with two missed cuts in a row before this week.
First-round leader Jimmy Walker could not repeat the magic of his opening course-record equalling 63, with a double bogey on the 11th leaving him two over on the day and seven under overall, alongside Harrington and Josh Teater, who went round in 72.
Defending Masters champion Phil Mickelson and last year's runner-up Lee Westwood continued their preparations for Augusta with rounds of 70 and 72 respectively to leave them both at four under par.