A glorious round of 65 that was typical Mickelson in its application - one long series of ups punctuated by the odd down, one long smile punctuated by the odd frown - sent him to seven under and a commanding clubhouse advantage over a group four long shots behind.
The left-hander has been around too long and seen too many surprise winners in the year's final major - such as Shaun Micheel in 2003 - ever to dismiss the merits of England's Lee Westwood, in the bunch on four under after a second 68, or even another lad from Nottinghamshire, Greg Owen, on three under after a 69. But he would not be human if he failed to highlight the obvious threat of the decidedly superhuman figure of Vijay Singh, who loomed most ominously of all on three under after a 67 that had title defence written all over it.
Neither would Mickelson have dared forget the name Tiger Woods, despite the world No 1 finding himself 13 shots off his breakneck pace last night when he set off on his second round. If that was not bad enough then the 29-year-old, who was still hell-bent on securing his third major of the season, was not being allowed to consign Thursday's 75 to the back of his seriously aggrieved mind as a storm of controversy was whipping up that suggested that Woods should even have been disqualified after an incident when his own caddie, Steve Williams, was speculated to have stepped on his ball.
The local newspapers here were full of it and as the Golf Channel was arguing over the "did he's" and "didn't he's" long it into the night, it was easy to forget that there was a golf tournament going on in the background. Until Mickelson's remarkable card presented itself, that is.
Starting on the 10th, the Californian whose record in the Grand Slam events thus far this campaign can be most kindly described as "unsatisfactory", was soon driving his overnight total of three-under deeper into the red with a wedge to five feet at the 11th and a quite joyous exit from a bunker on the 13th that yielded another birdie on the treacherous 13th. And when he streaked through the two par-fives that would usually close the round in three under - ramming home an 18-foot eagle putt on the 18th - he was eight under and charging.
But Mickelson would not be Mickelson if the route towards his second major was that straightforward. On the first (his 10th) he went from the thick stuff on the left to the thicker stuff on the other side of the fairway and the double-bogey that ensued jammed on the breaks. For then.
"I certainly didn't think I could shoot a 65 around here," he said, the perma-grin whiter than ever. "I just wouldn't have believed I could have shot enough birdies, especially seven of them and that eagle."
Indeed, it was spectacular stuff and a blessed distraction from yet another grotty affair that was threatening to drag the good name of golf into the mire again - namely "Ditchgate".
The circumstances were that on the 18th (his ninth) during Woods's calamitous first round, the misfiring favourite had watched his drive bounce off a tree to the egde of the water hazard that divides the fairway. On discovering the ball "plugged" into the wet soil, Woods and Williams claimed that it must have been stood on by a cameraman and asked for a free drop, which was denied, twice, by officials.
As the pair were adamant it had been trodden on and as his playing partner Kevin Sutherland agreed, the videos were poured over to see if anyone had indeed done so, intentionally or unintentionally.
But all these showed was that only Williams had gone remotely near the ball and one set of pictures even suggested that the caddie had stood on something when he made a step and appeared to pull his foot back.
The New Zealander denied it afterwards and so saved from Woods from an ignominious end to his 36th major. The penalty for stepping on your, or your employer's, ball, is a shot but as Woods had already signed for a six on that hole he would have been disqualified - not in the script that Mickleson was busy rewriting.
USPGA Championship (Baltusrol GC, Springfield, New Jersey) Early leading second-round scores (US unless stated): 132 P Mickelson 67 65. 136 R Sabbatini (SA) 67 69; D Love III 68 68. 137 S Appleby (Aus) 67 70; G Owen (GB) 68 69; V Singh (Fiji) 70 67. 138 Yang Yong-eun (S Kor) 71 6; G Ogilvy (Aus) 69 69. 139 K Perry 69 70; J Bohn 71 68; M Hensby (Aus) 69 70; S Ames (Can) 67 72.