HOUSTON - With another crack at the Masters looming, rising US star Jordan Spieth fired a five-under par 67 on Saturday to grab a one-stroke lead after three rounds of the Houston Open.

Spieth finished with six birdies and one bogey to build the 54-hole total of a 14-under 202 and was one stroke in front of Americans Scott Piercy, Johnson Wagner and Austin Cook. Piercy, who matched the course record with a 63 on Thursday before ballooning to a 74 on Friday, rebounded with a six-under par 66.

Wagner also signed for a 66 while Cook carded a two-under 70 to round out the group on a 203. Englishmen Kelvin Day and Paul Casey both shot 68s to head a group on 205, where they were joined by Charles Howell (69) and Russell Henley (68).

Phil Mickelson, whose game appeared to be coming around just in time for a run at a fourth Masters title, endured a tough day that included a double bogey and four back-nine bogeys -- three in a row to end his three-over 75. He was in a group on 208, six shots off the pace. "I didn't play well today," Mickelson said. "The last three bogeys hurt. I fought all day without really playing well to keep it at even par and then the last three holes got me." Spieth insisted that the availability of birdies on the Golf Club of Houston course meant his one-shot lead would mean little on Sunday.

"I'm not going to think about being up one, I'm going to think about playing the golf course," said the 21-year-old. "It's a bunched leaderboard with a lot of guys making birdies. I'm not necessarily the favorite tomorrow just being up one." If Spieth can hang on for a third US PGA Tour title, it will give him massive momentum heading into the first major of the year at Augusta National next week. Last year Spieth led by two strokes with 11 holes to play on Sunday at Augusta, but mid-round bogeys opened the door to eventual winner Bubba Watson.

Since then he has notched victories at the Australian Open and the unofficial Hero World Challenge hosted by Tiger Woods before adding a second US Tour title at the Valspar Championship and finishing second in the Texas Open this month. Spieth said accuracy off the tee was the key on Saturday. He hit 13 of 14 fairways in regulation and 16 of 18 greens. "I figured starting out today that the course would play tougher with this northeasterly wind," he said. "So I put a premium on driving the ball. I drove the ball extremely well to give myself some chances coming in."

After two birdies on the front nine, Spieth stepped it up coming in. He rolled in birdie putts of three feet and seven feet at 10 and 11, and picked up another stroke at the par-five 13th with a five-foot birdie. A three-putt bogey at the par-three 14th was the only blemish on Spieth's card, and he pulled the shot back with a 41-foot putt from just off the green at the par-three 16th.