The American, who started the final round on Sunday at Pebble Beach three shots back, ended with a three-shot lead with two holes left to play.
After a rain-delayed start, Mickelson had produced a blemish-free round and holed six birdies to move to 18 under at the top of the leaderboard before play was called off.
Third-round leader Paul Casey, who mixed two bogeys with two birdies, was at 15 under with three holes remaining, tied with Scott Stallings who finished with a 66.
Australian Jason Day and Si Woo Kim, of South Korea, were in the clubhouse on 13 under.
Scot Russell Knox closed at nine under after a fourth-round level-par 72, one shot clear of Northern Irishman Graeme McDowell.
Play will resume at 8am (4pm GMT) on Monday.