Harvard's sensational Danny Mahoney upset defending champion Dave Hawk of Cornell last night to win the one-meter diving chmapionship in the first day of the Eastern Intercollegiate Swimming tournament at Yale.

Mahoney, undefeated in regular season meets off the high board, had not competed in a low-board competition since last year. He poured in an impressive 369 points to top Hawk's total of 366. The Harvard senior is also favored in the high-board dive, his specialty, on Saturday.

Seventh Place

Harvard's other opening-day entrants did not gain the finals, but the Crimson was in seventh place after yesterday's five events. Yale won two events on its way to building up a commanding lead. Steve Clark took the 50-yard freestyle in 21.3, then came back with a 45.9 freestyle anchor lap to win the 400-yard medley relay from Army in a time of 3:35.3.

Tim Beard of Navy, who placed only third in the individual medley against Harvard in December, edged Yale's Ed Townsend to win the gruelling 400-yard individual in 4:26.9, breaking the old record held by John Pringle of Harvard. In the 500-yard freestyle, defending champion Harrison Merrill of North Carolina nosed out Princeton's Chris Brown to win in 4:58.1, also a new meet record.

In today's events, Neville Hayes is seeded first in the 200-yard butterfly on the basis of his performances this season. His clocking of 1:57.4, set against Navy in December, is a full three-and-a-half seconds better than the next best time, turned in by Tim Kennedy of Yale. Bruce Fowler and Bob Corris are strong throats to upset Yalis Dale Keifer, whom Corris edged last week, in the 200-yard breast-stroke.