Lefty was feeling a lot better'and still in the lead alone'when he finished the third round Saturday with a 17-foot birdie putt from the front edge.
A nice way to finish the round, Mickelson said.
Mickelson overcame an early bogey and some missed chances with seven birdies in his last 13 holes for a 5-under 65 that got him to 12-under 198. He led Rod Pampling (63) and Stephen Ames (64) by one stroke.
Pampling was on pace for a record-tying round at Colonial, the course near the Australian natives Flower Mound home that he gets to play often. But he had consecutive bogeys at 16 and 17 before hitting his approach at No. 18 within a foot for a birdie that left him two strokes off the tournament record.
Ames started with three birdies in the first four holes and finished without a bogey.
Tim Clark (64) was alone in fourth, three strokes back. Ben Crane (67), Kevin Sutherland (68) and Brian Gay (69) were at 203.
This is the 27th time Mickelson will lead going into the final round of a tournament, and this time he will be going for his second plaid jacket at Colonial. He has gone on to win 19 times, including the Northern Trust Open in February, his only victory this season.
The last six Colonial champions led or were tied for the lead after 54 holes. The last time that didnt happen was 2001, when then-defending champion Mickelson and Brett Quigley were tied going into the final round before Sergio Garcia won.
After hitting his first shot of the day into a fairway bunker and having to settle for par 5 on the opening hole, Mickelson was less than 30 yards from the flag after a 333-yard drive at No. 2. But he flubbed the chip shot, leaving it in the rough short of the green then two-putted from inside 8 feet for bogey.
When an 11-foot birdie chance at the 467-yard 3rd slid by the hole, after hitting a low-liner from the rough that rolled up near the flag, Mickelson shook his head in disbelief. The frustration didnt go away when a 24-foot birdie try at the difficult 252-yard par-3 4th stopped just short.
The first birdie for Mickelson finally came after his approach to 5 feet at the 394-yard 6th. But he missed an 8-footer on the next hole.
Mickelson hit his approach at No. 9 within 6 inches for a tap-in, the first of three consecutive birdies that got him to 10 under. He knocked his second shot 10 to 5 feet, and blasted from a greenside bunker at the 611-yard 11th to about 4 feet.
A bogey followed at No. 12, when he decided to chip instead of putt from the front fringe and knocked it 8 feet past the cup. He saved par out of the greenside bunker at the par-3 13th by hitting inside 3 feet before two more birdies, with approach shots inside 10 feet at Nos. 14 and 15.