By Andrew Both

HUMBLE, Texas (Reuters) - American Bryce Molder has never won on the PGA tour, but if the golfer can maintain his lead at the Shell Houston Open he will earn an invite to next week's U.S. Masters.

Halfway leader Molder and his closest pursuers -- Cameron Percy and Alex Prugh -- are not exempt for the opening major of the year at Augusta National in Georgia, and the only way they can get there is to win here at Redstone Golf Club.

"If you tell me not to think about next week, or I'm trying to tell myself, well I'm still thinking about next week," Molder told reporters on Friday. "Put me on top of a building and tell me not to be scared, I'm still going to be scared."

Molder matched the day's best score with a bogey-free 66, to set the pace at nine-under 135. Fellow American Prugh also carded 66 to join Australian Percy (69) at eight-under.

Percy was certainly not afraid to admit he too was thinking about earning a last-minute ticket to the Masters.

"Anyone in my position would be thinking about it," he told reporters. "It would be a dream come true to ring up my mates and say 'come over next week.'"

Lucas Glover aced the par-three 16th with a six-iron, making him the first player to record a hole-in-one since the Houston Open moved to its current venue in 2006.

Not long afterwards, Woody Austin aced No. 7.

Several big names who came here to tune-up for the Masters had their preparation shortened by missing the cut.

Among them were Australian Geoff Ogilvy, who double-bogeyed the last hole to bow out, German Martin Kaymer and Northern Irishman Rory McIlroy.

Ernie Els and Phil Mickelson both advanced to the final 36 holes despite frustrating days.

Els shot 74 to fall nine strokes behind, a stroke better than Mickelson, who carded a 76 that included an unusual triple bogey at No. 10.

After pulling his drive into a bush, the lefty Mickelson took a right-handed swipe at the ball. However, the ball popped out and him on the leg before ricocheting back into the bush.

Mickelson was penalized one stroke for being hit by the ball and decided to take a further one-stroke penalty so that he could drop his ball clear of the bush.

(Editing by Frank Pingue; To query or comment on this story email sportsfeedback@thomsonreuters.com)