Jorge Jesus' side, top of the Saudi league and still alive in the King's Cup and Asian Champions league, are bidding for a quadruple of trophies this season.
Al Hilal took an early lead after five minutes through Malcom following a one-two with Saleh Al Shehri.
"It was a tough game, delighted to score two goals, and we were thrilled to secure our first title of the season. We have other trophies to pursue," Malcom told SSC Channel.
Abderrazak Hamdallah equalised in the 21st minute as he struck from the rebound after his penalty was saved by Al Hilal's Yassine Bounou.
Al Hilal went ahead again when Salem Al Dawsari struck from the edge of the area in the 44th minute, Malcom scored from close range after dribbling past Al Itthad captain's Ahmed Hegazy and substitute Nasser Al Dawsari completed the rout.
The rivalry between Al Hilal and Al Ittihad will be renewed in the King's Cup semi-final on April 30th.