DULUTH, Georgia - In-form Phil Mickelson tightened his grip on the BellSouth Classic with five consecutive birdies on Saturday to forge 11 strokes clear midway through the third round.

Six ahead overnight at the TPC at Sugarloaf, the defending champion raced to the turn in five-under-par 31, leaving his challengers trailing in his wake.

At 21 under overall, the American left-hander is on track to shatter the tournament record for 54 holes.

Compatriot Larry Nelson holds the mark with a 21-under total of 195 in 1988 when the event was played at Atlanta Country Club.

The PGA Tour record of 24-under 189, achieved three times on par-71 layouts, is also under threat.

Jose Maria Olazabal, playing with Mickelson in the final group, was tied for second at 10 under, having sandwiched birdies at the fourth and sixth around a bogey-five at the sixth.

Level with Spaniard Olazabal were Americans Doug Barron, Zach Johnson and J.J. Henry.

Barron was seven under for the day after 16 holes, Johnson five under after 11 and Henry level after nine.

Of the other big names competing in the final PGA Tour event before next week's US Masters, world number three Retief Goosen was at nine under after 12 holes with Ireland's Padraig Harrington a further two strokes back, after 12.

Mickelson, who won the first of his two BellSouth crowns in 2000, parred the first two holes before easing into overdrive.

The twice major champion picked up his first stroke after hitting his approach to 10 feet at the par-four third. That soon became a two-shot swing when playing partner Henry, alone in second place overnight, bogeyed the hole.

Despite finding the right fairway bunker off the tee at the par-five fourth, Mickelson laid up in two before hitting a pitching wedge to within four feet of the flag for birdie number two.

He then rolled in a 20-foot putt on five, got up and down from the left of the green at the par-five sixth and coolly sank another 20-footer at the seventh to get to 21 under.

Surprisingly, Mickelson collected his first bogey in 37 holes when he three-putted the par-three eighth after his tee shot finished 85 feet short of the hole.

Bidding to become the first repeat BellSouth winner since American Hale Irwin in 1977, Mickelson coaxed in a 15-footer for birdie at the par-four ninth to stretch his lead to 11.