John Cook scorched Plainfield Country Club's back nine in the morning with five birdies and went on to defeat Scott Hoch, 5 and 4, in the scheduled 36 hole final of the 78th U.S. Amateur golf championship yesterday.

Cook, 20, two-time Ohio State All-American from Dublin, Ohio increased a one-hole lead to six during a torrid stretch when he birdied holes 10, 11, 13, 15 and 16.

After winning the first three holes on the back nine, the lanky blond seemed to say, "Anything you can do, I can do better" on the par-4 13th hole when he faded a long, high iron shot over a trap. The ball nestled six feet from the pin, after Hoch had hit within 12 feet. Cook sank the birdie putt for a 5-up lead.

Hoch sank a 30-footer for winning birdie on the Par-3 14th, but Cook regained a 5-up advantage with a 25-foot birdie on 15 and went 6 up with a six-footer on 16.

The only poor shot Cook hit during those nine holes was on 17, where he duck-hooked his drive and lost the hole to Hoch, last year's Atlantic Coast Conference and Northeast Amateur champion from Raleigh, N.C. They halved the 18th hole in par and Cook led, 5 up.

During the lunch break, a green-skeeper mistook Hoch for Cook and said, "Hurry up and get it over with, I'm tired."

Hoch appeared to be cooperating when he drove behind trees to the right on the first hole in the afternoon and fell 6 down. Hoch, who eliminated Bob Clampett in the semifinals, had driven out of bounds on the same hole in the morning.

Cook moved 8 up with an eight-foot birdie putt on the third hole.

Cook's game lost its keen edge after that and Hoch reduced the margin to five holes when he won the 13th with bogey. The match ended on the 14th hole, where Cook scored regulation par.

Cook averaged 72 strokes for 32 Big Ten matches this spring, one-tenth of a stroke higher than Jack Nicklaus did in his best year at Ohio State.