Villanova (9-0) converted 30 of 31 second-half free throws, including 29 in a row, to win the area's most intense rivalry. The Wildcats won for the 43rd time in 57 meetings against the Hawks (3-5).
Idris Hilliard scored a career-high 22 points, and Darrin Govens added 19 for St. Joseph's, which had five players with at least 12 points.
St. Joe's charged within four points with less than two minutes to play. But King, a transfer from Duke, drilled his fourth 3-pointer with 1:29 left to give the Wildcats breathing room. Corey Fisher also drilled four straight free throws when the Hawks were forced to foul.
The Wildcats trailed 38-37 after Govens turned a Bryant Irwin pass into a reverse lay-up with 2:41 left in the first half. But Reynolds drove for a lay-up on the next possession and Villanova never trailed again.
The 38 points were the most given up by the Wildcats in an opening half this season.
After St. Joe's pulled within 1 by hitting the first basket of the second half, Villanova went on a 16-7 run over the next 6 minutes, building a 10-point lead. Their biggest lead of 12 points came after freshman Dominic Cheek scored on a lay-in with 7:44 left.