Ryan Palmer holds a two-stroke lead over the field after the second round of the Valero Texas Open.

Palmer, who shot four under in round one, finished with a six-under 66 to move to 10 under.

The American finished the round bogey-free, and three times carded back-to-back birdies on the second and third, eighth and ninth, and 14th and 15th.

Speaking to the media after his round, Palmer said the key to his success is to limit the severity of his mistakes.

"It's a golf course – if you get it off-line, you're going to struggle," he said. 

"I was able to keep the ball in front of me. When I've missed fairways, I've gotten fortunate breaks, I think. 

"[This] weekend, it's a matter of just avoiding those big misses."

Kevin Chappell worked his way into a three-way tie for second after he shot 65 for the best round of the day, and he is joined at eight under by South Africa's Dylan Frittelli and American Matt Kuchar.

Chappell – who is ranked as the world number 547 – played the course beautifully, nabbing an eagle on the par five second hole before going bogey-free and birdieing the eighth, ninth, 12th, 15th and 17th.

The leader after round one, Russell Knox, had a poor day, bogeying four of his first six holes on the way to shooting 76, dropping down to three under and a tie for 27th.

With the cut-line at even par, Jordan Spieth followed up his even par first round with a 70 on Friday to sneak into the frame.

Plenty of notable names who will hope to contest the US Masters crown next week failed to make the cut, including Jason Day, Rory McIlroy, Rickie Fowler and Bryson DeChambeau.