Phil Mickelson has boosted his preparations for next week's Masters at Augusta by taking the lead at the halfway point of the Shell Houston Open.

The 44-year-old got his round off to strong start by birdieing the second before giving back that shot at the next hole.

However, further birdies at the fourth, fifth and ninth holes saw the former world number one reach the turn in 33.

Mickelson, who carded an opening round of 66, picked up further shots at 11, 13 and 15, but bogeyed the 17th to drop back to 11-under-par and leads by one stroke from Canadian Graham DeLaet.

DeLaet put himself in contention heading into the weekend after registering a second consecutive round of 67 at the GC of Houston.