King, a transfer from Duke, scored 20 points and hit two key 3-pointers in the closing minutes to lead the No. 3 Wildcats past St. Joe's, 97-89 on Wednesday night.
"In some ways, it was like a bout," Hawks coach Phil Martelli said. "They took a swing. We took a swing."
Scottie Reynolds had 22 points, and Antonio Pena chipped in with 15 to help the Wildcats win the area's most intense rivalry.
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.
"It was crazy, but I treated it like any other game," King said.
Villanova (9-0) converted 30 of 31 second-half free-throw attempts, including 29 in a row, to win for the 43rd time in 57 meetings against the Hawks (3-5).
"That was big," Villanova coach Jay Wright said. "We have good shooters. In the second half, every one was big."
St. Joe's charged within four points with less than two minutes to play. But King drilled his fourth 3-pointer with 1:29 left to give the Wildcats breathing room. Corey Fisher also made four consecutive free throws when the Hawks were forced to foul.
"He's a marvelous player," Martelli said. "He has a quick release, a pretty shot and incredible passion."
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 one by hitting the first basket of the second half, Villanova went on a 16-7 run over the next six 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.
"I say it every time," Wright said. "You can never predict these games. You've got to tough it out. They really played hard and I'm proud of our guys. They played great and we gutted it out."