By Larry Fine

SPRINGFIELD, New Jersey (Reuters) - Phil Mickelson thinks a major championship record low round will be shot at Baltusrol Golf Club over the last two rounds of the PGA Championship and that someone might take it as low as 61.

Unheralded Robert Streb became the 28th player to match the record low of 63 at a major in Friday's second round on the rain-softened, par-70 layout to share the midway lead with fellow American Jimmy Walker at nine-under.

Mickelson shot 63 in the opening round of the British Open two weeks ago at Royal Troon, and Big Lefty was beaten in a sensational final-round duel there by Sweden's Henrik Stenson, who fired his own 63.

"I think that major record of 63 will be broken today or tomorrow," Mickelson told TNT after shooting 68 in the third round.

"I think there's a 61 or 62 out there because it's par 70, the greens are pristine – they're rolling beautifully – and they're soft.

"There's just a lot of birdie holes."

Mickelson, who won the 2005 PGA Championship in the last major contested at Baltusrol with a four-under total, said showers had changed the character of the course.

"The rain (Friday) really changed the way it's played," Mickelson said. "And it's taken a lot of the fire and the speed out of the greens and it's also softened the fairways to where balls stay in the fairways.

"So you're going to hit a lot of fairways and the ability to hit 6-, 7-, 8-iron at the pin and have the ball just stop right by its divot is taking away the challenge of the greens."

Such a round may not come on Saturday, as the threat of lightning in the area caused a suspension of play before co-leaders Walker and Streb had teed off.

Possible thunderstorms were also in the forecast for Sunday.

Five-times major winner Mickelson, whose birdie putt for the elusive 62 at Royal Troon veered away from the cup at the last instant, bogeyed the first on Saturday, two strokes better than his self-described "horrendous" start on Friday, but came back with four birdies in posting his two-under 68.

Three-times major winner Padraig Harrington of Ireland showed low scores were available in the early going on Saturday with a five-under 65 that moved him to four-under for the championship.

American Kevin Kisner also shot 65 to reach five-under for the tournament.

(Reporting by Larry Fine; Editing by Mark Lamport-Stokes)