McIlroy notched his fourth victory this season and sixth time of his PGA Tour career and solidified his position in the driver's seat of the FedEx Cup race heading into the Tour Championship.
Westwood registered a 3-under 69, while Mickelson posted a 2-under 70 in Sunday's final round.
Mickelson gained the fourth spot on the playoff list with the performance.
Dustin Johnson and Adam Scott each turned in 70s Sunday to end knotted for sixth at minus-16.
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