Paul Cayard predicted a dogfight if his AmericaOne and the Italian boat Prada made it to America's Cup challenger finals, but he never said it would be pit bulls in a bad mood.

The tightest race so far in the semifinals turned on back-to-back umpires' calls today, as Cayard and Prada skipper Francesco deAngelis forged downwind on the final leg, overlapped and almost touching under straining spinnakers, with both crews shouting their lungs out in protests to umpires alongside.

First the umpires saw it Cayard's way, then deAngelis's. The two penalties in close maneuvers offset each other, and AmericaOne managed to squeeze out an eight-second victory. It left the Italians muttering and Cayard advising his crew, some of whom are in their first Cup season: "That's a little preview of what's to come, guys. Just a preview."

As the twin, 75-foot racers sailed back to harbor side by side, neither acknowledging the other after the acrimonious finish, Cayard pointed to the dispirited Prada and said to his crew: "There's a world of hurt on that boat. That's a hurt-locker over there."

But what a race they had had, with so much on the line.

The win guaranteed AmericaOne (7-1) at least a tie for one of two spots in the challenger finals that begin Jan. 25. Meantime, Prada, which had the best record by far in two months of preliminary racing at 26-3, now stands a disappointing 5-3 in the semifinals, just one worrisome point ahead of Dennis Conner's Stars & Stripes and Japan's Nippon, both of which won today.

With two races to go, Prada will have to fight to make the finals.

Even more important to AmericaOne than the win was the way it was accomplished--first with blazing speed, then as the wind dropped with a gut-wrenching, come-from-behind tactical triumph that had Cayard at one point asking tactician John Kostecki, "Are you nervous?"

He should have been after the turnaround in fortunes. AmericaOne walloped Prada up the first leg of the course and shot out to a one-minute lead that had most spectators on a breezy, sunlit day convinced the race was over at the first turning mark.

Sailing parallel courses, AmericaOne climbed right away from Prada, partly because of a beneficial wind shift but largely because of better speed in the breezy conditions and an apparent ability to sail at a higher angle to the incoming wind.

The race appeared to be over with a one-minute AmericaOne lead at the first turning mark, but as the wind dropped from 15 knots to 10, Prada came steaming back. The Italians cut the edge in half on the second downwind run, then hammered away up the last upwind leg, digging bit by bit into what was left of the lead as AmericaOne struggled with a poor choice of headsails.

By the time the two boats hit the last turn, they were overlapped. DeAngelis, who has sailed extensively with Cayard in big boats around the world, outfoxed his old shipmate, got inside at the mark and rounded six seconds ahead.

But Cayard roared back and the two boats danced down the final run in lockstep, AmericaOne's bow seemingly glued to Prada's transom, with the crews bellowing protests to on-water umpires, each demanding that the other sail his proper course to the finish, rather than ducking and weaving to slow the other boat.

Eventually the umps flagged Prada for sailing below proper course, then they flagged Cayard.

When the flags stopped flying, the penalties had offset each other and Cayard had the lead, barely, and held off the rushing Italians for the crucial win. Prada, the $50 million, two-year program that set the standard for all challengers with its exhaustive nature, now faces Le Defi France and Nippon in its remaining semifinal races and must win both to ensure an advance to the finals.

Cayard is guaranteed at least a tie for a top spot, and with one more win is ensured a place in the best-of-nine challenger finals. The winner goes on to race Team New Zealand for the Cup Feb. 19.