South Korea's Sung Kang shot a 10-under 61 in tough conditions to vault to a four-stroke lead at the halfway mark of the AT&T Byron Nelson in Dallas.

Kang said he could hardly move his body on an unusually cold May day in north Texas but notched six consecutive birdies en route to a 16-under 126 total at Trinity Forest.

Americans Matt Every (65) and Tyler Duncan (66) were tied for second on 12-under, with big gun Brooks Koepka (66) a stroke further back.

But former Dallas Cowboys quarterback Tony Romo will be benched on the weekend, after carding a 74 to miss the cut by 10 strokes.

"I live in Dallas and I've never seen the weather like this in May," said 31-year-old Kang.

"I checked the weather yesterday and I knew it was going to be really cold and windy so I tried to prepare for how far the ball was going to go this morning and it worked out great."

World No. 138 Kang has not had a decent result since a tie for sixth at the Arnold Palmer Invitational in March and is seeking his first PGA Tour win.