England international James stepped up to produce an inspirational display as the Blues got their hands on the trophy for a fourth time.
This despite the Londoners being without their Australian international duo Ellie Carpenter and Sam Kerr, who were away on Matildas action in the Women's Asian Cup.
Speaking before she left for the tournament in Perth, Carpenter confirmed she would be supporting her team-mates from afar.
And she would have been delighted to see James, who joined Chelsea from United in July 2021, displaying her usual combination of poise and predatory instincts to net the opener in the 19th minute.
The 24-year-old pounced on a terrible error by United's Dominique Janssen, snapping up the Dutch defender's under-hit back-pass from a throw-in before driving into the box and rifling past Phallon Tullis-Joyce for the opener.
James lit up the game in the first half, her willingness to pass, shoot and dribble with either foot causing no end of problems for the United defence.
That said, United had plenty of chances of their own in the opening 45 minutes but their finishing lacked the precision needed to beat Hannah Hampton and their second-half attempt at a comeback lacked energy as they struggled to exert pressure on the Chelsea goal.
Aggie Beever-Jones put the game beyond doubt in the 77th minute, toe-poking the ball home after good work by Swedish winger Johanna Rytting-Kaneryd to set her up, as Chelsea held on comfortably to claim the first silverware of the season.
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