Francois BRENAC (FRA), the opening day co-leader sailing Benjamin COHEN's (FRA) French entry, led the 58-boat fleet across the finish line in Wednesday's second race but was disqualified for failing to restart after starting early.
That misstep elevated PORTER, of Winnetka, Illinois, to the top as the only boat with all single-digit finishes: 3,5,3,6 for 17 points, eight ahead of defending champion Nicola CELON (ITA).
Dave ULLMAN (USA) posted his second consecutive win by a full minute in Wednesday's first race but slipped to 11th in the second.
PORTER's tactician is Harry MELGES III (USA), who won the 2002 Melges 24 Worlds at Travemunde, Germany, and his brother John and Andy BURDICK (USA) - class veterans all - complete the crew.
'We've had three good starts so far,' PORTER said, 'Then a horrible start in the last race. But we got lucky when [the wind] came left. We started to go back to the right - 80 per cent of the time on a normal day at Santa Cruz that's the place to be - and Harry saw some more wind on the left.'
With the wind shifting, most of the fleet wound up in the middle of the course on the third and last beat because, PORTER said, 'I don't think anybody knew where to go.'
Wednesday's races were sailed in southwest winds of 5-14 knots with a ring of light fog around the course partially obscuring the shores of Monterey Bay. Each race had a general recall before getting under way under I-flags, plus a Z-flag calling for a 20 per cent penalty for starting early.
But BRENAC took the worst hit. Apparently headed for his second win in two days, he heard no finishing horn as he crossed the line 28 seconds ahead of Stuart SIMPSON's (GBR) boat The Barbarians. Later, he was recorded as OCS at the start but failed to return, calling for disqualification and handing the victory to SIMPSON.
Nine boats started early but three, including BRENAC, failed to return.
'I don't know why he didn't restart,' principal race officer Hank STUART said. 'His [bow number 28] was called twice on the radio.'
BRENAC was not immediately available for comment.
Joe Fly helmsman Gabrio ZANDONA (ITA) could empathize with his rival. The Italians, expected to be title contenders here, had to restart both of Tuesday's races and logged a 28 and a 24. They came back Wednesday with a 9 and 6, but ZANDONA was not encouraged because there is only one throwout in the ten-race schedule.
'We had nice starts today,' ZANDONA said with half a smile, 'So we had a chance to make a race. But we are out of the game.'
Samuel (Shark) KAHN (USA), the 2003 champion, also bounced back with an 11 and a 9 after a similar double starting bobble Tuesday - a 29 and a 23 - and shares Joe Fly's predicament.
Meanwhile, Mark (Crusty) CHRISTENSEN (USA) leads the four-boat Team Pegasus effort in third place, although his entry was almost an afterthought. CHRISTENSEN's crew is Pete SPAULDING, Brian LEE, Arthur KINSOLVING and Shane ILIIDGE. All but SPAULDING - a fifth-place finisher in the 2004 Olympic Games sailing a 49er - work fulltime for Fullpower, the title sponsor.
'We didn't have very high expectations because the first time we've sailed together was in the Pre-Worlds,' CHRISTENSEN said. 'I had sort of stopped sailing.
'Then Philippe [KAHN] said, 'If you like you can take my old boat,' so I thought it could be fun.'
Racing continues through to Saturday. The only throwout kicks in after the sixth race on Thursday, which could scramble the upper echelon.