The two top-rated U.S. teams scored convincing double victories today as the 4 1/2-month-long run-up to the 30th America's Cup opened under cloudy skies and spitting rain.

Paul Cayard's AmericaOne and the New York Yacht Club's Young America managed comfortable back-to-back wins in light to moderate winds on the first day of challenger trials, while Dawn Riley's America True went down to double defeat.

Elsewhere on the water, the sleek, silver Italian entry Prada also had an upbeat day, beating the overmatched Swiss boat FAST 2000 by a convincing four minutes in the first race, then easily topping Nippon in the afternoon.

But the Italian effort was not without drama. The crew dropped its spinnaker overboard nearing a mark with Nippon four lengths behind and had to cut the big sail and leave it floating behind to be picked up by a support crew on a tender. A crewman went overboard briefly in the fracas but was hauled back on deck. It was an embarrassing foul-up for the Italians, who have been practicing for this regatta for three years, longer than anyone.

"It was a big mess," skipper Francesco de Angelis said. "He got caught in the jib sheet and went over, but we caught him." To hold on to the lead, he said, "We had to do a hard job instead of the easy one."

Among the five U.S. boats, only America True wound up winless, losing first to Young America, then to AmericaOne. "We're either going to be a little happy, a lot happy or very unhappy," the San Francisco-based Riley said before setting off onto the Hauraki Gulf to test her new yellow yacht in battle for the first time. She had the toughest draw of the opening day.

The second loss was particularly galling to helmsman John Cutler, who let AmericaOne skipper Paul Cayard force him over the start line early, and had to go back and restart. "We gave them a little head start and that was too much with those guys," he said.

Cup legend Dennis Conner had a scare in his only race as his Stars & Stripes beat the French entry Le Defi Francais by a scant nine seconds after leading comfortably in the early going. The French, benefiting from a favorable wind shift, caught up on the last leg and nearly passed Stars & Stripes, which had a bye for the afternoon racing.

Hawaiian entry Abracadabra, under Olympic silver medalist John Kolius, split its pair, losing by 38 seconds in a close match to Nippon in the morning but easily beating FAST 2000, with its radical twin keels and twin rudders, in the afternoon.

It marked the first time for two-a-day America's Cup trials. The 11 challengers agreed to cut down the length of races from 18.5 miles to 13.5 and double up the daily grind for this first round, in an effort to get a quick handle on where they stood relative to the field. The week-long round will likely be followed by frantic efforts to upgrade among those that turn out to be off the pace.

The start of racing followed a festive weekend at the Viaduct Basin at the foot of Auckland's busy business district. Crowds of sailing-mad New Zealanders on both days jammed the America's Cup Village, where all 11 challengers and Cup defender Team New Zealand have set up compounds.

But the crowds were back to work this morning and only a few hundred spectator craft dotted the water as the challengers filed out of the basin and headed to sea to begin the process of winnowing down the challenger field to one, with the winner to face Team New Zealand in the 30th Cup match in February.

If this was to be the challengers' day, a bit of their thunder was stolen by Team New Zealand, which sent both of its new Cup defense contenders out for a day of sail testing and crew training. The two black Kiwi boats sailed past the challengers' race course, passing notice that they are up and running ahead of schedule in the quest to successfully defend come February.

"People were going around saying we wouldn't have boats in the water until December," crowed Team New Zealand tactician Brad Butterworth. "We're just a month and a half early." The latest of the New Zealanders' two new Cup boats, NZL 60, was launched Saturday and had its first sea trials today, sailing side-by-side with its stablemate NZL 57 in sight of the challengers.

The double victory by Young America bodes well for the charcoal gray entry of the New York Yacht Club, whose speed was unknown as the crew had avoided contact with any other boats until today.

If Young America continues to do well, others may try to match its unique, wing-like mast, one of the technological surprises of the new Cup season. The carbon fiber spar on Young America is about twice as wide as a standard Cup mast, a feature designer Bruce Farr hopes will make it stiffer when Auckland's harsh breezes blow up, as they are expected to do later this week.

Today, Young America skipper Ed Baird managed to keep the boat well ahead of the competition from start to finish in both races in easterly winds of 8 to 12 knots, beating America True in the morning by 37 seconds and the Spanish boat Bravo Espana by 1 minute 49 seconds in the afternoon.