Lanny Wadkins birdied six of his last nine holes and tied the Magnolia course record of nine-under-par 63 yesterday to come from five strokes behind third-round leader Scott Hoch and win the $400,000 Walt Disney World Classic at Lake Buena Vista, Fla.

Wadkins, who moved into the lead in the player-of-the-year competition with his one-shot victory, hit into rough on the first hole and near a tree on the second, but then birdied No. 3 and eagled No. 4 and was on his way. Wadkins, earning $72,000 for the 15th victory of his career, third this year, ended at 21-under-par 267 for the tournament played on three courses with everyone at Magnolia for the final round.

Wadkins brought his PGA Tour earnings to $443,313 for 1985 and more than $2.3 million for his career.

Wadkins started the day fifth but passed four players, including Hoch, who closed with a 69, and Mike Donald, whose 67 tied Hoch for second place . . .

Mike Fetchick celebrated his 63rd birthday by winning his first event in six years on the PGA senior circuit, shooting par 72 for a six-under total of 210 for the 54 holes of the $200,000 Hilton Head Seniors Invitational. Defending champ Lee Elder was at 214.