HOUSTON (Texas) (AFP) - Phil Mickelson , warming up for his Masters title defense, fired his lowest round in two years Saturday to seize a share of the Houston Open third-round lead. Mickelson equalled the Redstone course record with a bogey-free nine-under par 63 for a 13-under total of 203. He was joined atop the leaderboard by fellow 40-something American Scott Verplank, who posted his second straight 65. Australian Aaron Baddeley carded a 66 and overnight leader Chris Kirk a 69 to lie one shot back on 204. Defending champion Anthony Kim of the United States (69) and Canadian David Hearn (66) followed on 205. Mickelson 's effort tied the course record set by Johnson Wagner and Adam Scott in 2008 and matched by Jimmy Walker on Thursday. It was Mickelson 's best score since a 62 in the third round of the 2009 Northern Trust Open at Riviera, which he won. Mickelson has managed only six top-10 finishes since claiming his third green jacket at Augusta National last April. But he put himself in prime position to seize a victory, especially since in the last four events in which he had a round of 64 or better, Mickelson has emerged with the title. While Houston Open organizers have tried to attract players tuning up for the Masters by emulating the conditions they'll face at Augusta National, Mickelson said he was more concerned with visualizing whatever shots he needs than with practicing specific shots. "What I'm working on is what I did best today, which was really seeing the shot and executing and holding that picture throughout the swing," Mickelson said. "I probably did that better today than I have in a long time." The player said a victory before the first major of the year could only be a good thing. He won on the US tour the week before he won the 2006 Masters. "People have talked about winning the week before a major as not necessarily the greatest thing, because it takes away energy, or what have you," Mickelson said. "I felt like in '06, it was really a benefit to gain the momentum and confidence of winning a golf tournament right before, especially the Masters." In cloudy, calm conditions, Mickelson birdied three of his first four holes. Paired with England's world No. 2 Lee Westwood, Mickelson sent his ball left off the sixth tee, and took a drop. However, he saved par by chipping in from behind the green. Verplank, who has been battling a sore left wrist, is making just his fourth start of the year. Even so, he has hit 34 of 42 fairways so far this week.