The two co-favorites in America's Cup challenger semifinals went down to defeat today, leaving just one unbeaten team in the regatta after two days of racing.

Dennis Conner's Stars & Stripes was the unlikely, uncontested leader in the standings after handily defeating top-rated Italian entry Prada. It was the second straight day Stars & Stripes scored an upset and the second time in 2 1/2 months that Conner's team beat the Italians, who have only lost two other races all season.

Meantime the other co-favorite, Paul Cayard's AmericaOne, had a 40-second lead over U.S. rival America True two-thirds of the way through their race on the Hauraki Gulf when strong winds ripped AmericaOne's headsail out of its fastenings and over the side, ruining enough gear in the process that the crew could not set a replacement and True went rocketing past to an easy win.

After two days of 10-day semifinals, that left only Stars & Stripes unbeaten at 2-0. It's a remarkable beginning for a team that made it into the semifinals with the next-to-worst record of six contenders, one of the smallest budgets and a stripped-down, one-boat campaign.

But today's win was no fluke. Conner, well into his fifties and the world's most experienced Cup sailor, doesn't sail on the boat anymore, preferring to run operations from ashore, but still sends veteran tactician Tom Whidden to call the shots, and for two straight days Whidden has done the job with great success.

With 20-knot breezes whipping the gulf into whitecaps, Stars & Stripes helmsman Ken Read carved an even start alongside the sleek, gray, elegant Prada and quickly forced rival helmsman Francesco de Angelis to tack away for clear air. Whidden had Read tack also, to stay atop his foe, and just as he did so a favorable wind shift lifted Stars & Stripes into a two-boat-length lead.

It was a near mirror of Whidden's perfect tactical calls the day before, when Stars & Stripes easily beat the highly rated Japanese entry Nippon.

But the race was far from over with 18 miles to go. Everything from that point on went Stars & Stripes' way. Prada, noted for smooth crew operations, first broke a vang fitting that helps hold down the mainsail, repaired it with duct tape, then twice had trouble setting a spinnaker and fell farther behind.

Strong winds whipped in from the southwest all day and the sky was a mass of dark, confused, speeding clouds. The challenging conditions proved too much for Cayard's crew on AmericaOne, widely regarded as the best sailing team in the regatta.

They looked it early on as Cayard forged a 35-second lead at the first turning mark on the strength of superior boat speed and crew work, then lost most of the lead when the crew failed to set the spinnaker correctly for the downwind run. It was tangled in the rigging and the mess took three minutes to sort out, with the mixed male-female crew on America True gaining back much of what it had lost.

AmericaOne's spinnaker work proved flawed twice more on the run, and by the second turning mark Cayard was fuming and tactician John Kostecki was shouting over the din of strong winds, "Work on your steering!"

Cayard did, and restored the lead to 27 seconds, but lost it all after the next downwind run. Cayard turned his boat to head back upwind, the crew hoisted a jib and everyone looked in horror as strong winds jerked it from the groove that connects it to the headstay, destroying the groove in the process so no replacement sail could be set.

Bowman Curtis Blewitt could be seen shaking his head in disgust as bright yellow America True streaked past to certain victory.

In today's other race, Nippon beat the French Le Defi Francais, a light-air specialist that was sorely overmatched in today's heavy winds.

The Standings

Semifinals at Auckland, New Zealand

Team R W L Pts

Prada 1 1 0 1

AmericaOne 1 1 0 1

Stars & Stripes 1 1 0 1

America True 1 0 1 0

Le Defi Francais 1 0 1 0

Nippon 1 0 1 0

Yesterday's Results

Prada def. America True by 1 minute.

Stars and Stripes def. Nippon by 55 seconds.

AmericaOne def. Le Defi Francais by 22 seconds.