Three teams headed to sea this morning to fight for survival in the waning days of the America's Cup challenger semifinals. They got survival conditions with over 20 knots of wind on foam-flecked, breaking seas; only two made it through, one by the slimmest of margins.

Prada, the top-rated Italian entry that entered these semifinals with the best record in the fleet but has struggled lately, staved off a relentless attack by European neighbor Le Defi Francais to win by nine seconds and maintain a one-point lead in the fight for the last spot in the two-boat challenger finals.

Dennis Conner's Stars & Stripes also won, holding off repeated attacks by California rival America True, which gained on every downwind leg but not quite enough to overtake the dark blue racer from San Diego. Stars & Stripes's final margin was a comfortable 46 seconds, but several times on this wild and windy day skipper Ken Read was barely able to cross in front of True.

Nippon was the one to fall off the track to the finals on a day so breezy and wet that Olympic gold medalist Thierry Pepponet, tactician on the French boat, was on his knees bailing seawater from the bilge with a bucket. He was not alone.

On Nippon, Prada, and Stars & Stripes, green rollers broke over the bows as an easterly low swept in from the Tasman Sea, pushing Hauraki Gulf into lumpy breakers that splashed in the cockpit to be removed by hand the time-honored way. It was an old-fashioned gear-buster day, but after two months of racing, the challengers have had time to hone their skills and no mistakes were major.

The big winner was AmericaOne, which eliminated Nippon with a 17-second win, ensuring itself of the top spot in the two-boat finals. San Francisco skipper Paul Cayard ran his fleet-best record to 8-1 with one race to go, his only loss in the semifinals coming on a gear breakdown late in the second race. Even then he was well ahead.

But beating Nippon was not easy. The Japanese team with veteran Australian skipper Peter Gilmour at the wheel went well upwind in the rough water and heavy winds, rounding the first mark just ahead of AmericaOne after a long drag race up the course.

Cayard, who on Tuesday roared up from behind on the last leg to hand Prada an eight-second loss in a race that looked more like naval warfare than yachting, did it again. He rallied alongside Nippon on the first downwind run, outmaneuvered Gilmour as they approached the turning mark and used the right of way to get the inside line and round the mark first.

As the boats turned back upwind, tactician John Kostecki had Cayard force Nippon to the right while AmericaOne went left to a favorable breeze. When they reconvened, Cayard had a handy, five-boat-length lead, all he needed.

The win means Cayard, his spot in the best-of-nine challenger finals secured, can choose whether to sail his last scheduled race Thursday against Stars & Stripes. Many observers reckoned he will stay at the dock, protect his assets and give the win to Stars & Stripes, which stands one point behind Prada in the run for the other finals spot. But tonight, Cayard said he was inclined to sail unless the conditions were very windy and he would be risking damage to his boats.

Stars & Stripes, which postponed one race last week after being damaged in a collision, has five points in hand and two races to go; Prada has six points but one race left. The final spot is still up for grabs between two teams from opposite worlds.

Stars & Stripes is a bare-bones, $10 million operation with a boat that was launched in September and a team of grizzled Cup veterans cobbled together at the last hour. Tactician Tom Whidden didn't even arrive until November, after the first round of trials.

Prada is the best-heeled, best-prepared challenger with a budget of more than $50 million and two boats launched in Europe last June. The team has been together 2 1/2 years, testing and training first in old boats in the Mediterranean, then here in the new ones.

Prada must beat Nippon Thursday to get to seven points; Stars & Stripes must beat AmericaOne, if Cayard elects to race on Thursday, then America True on Friday to get to seven. If they end up tied, they will race to determine the finalist.