His seven under par round of 63 at the PGA National Championship course in Palm Beach Gardens, Florida, was only bettered by Tiger Woods who shot a 62.
Far from perfect conditions on Sunday made the Worksop golfer’s round even more special.
Westwood opened the event with a level par 70, and followed that with a two-birdie, one-bogey 69 on day two.
Making the cut with ease, he again shot a level par 70 on Saturday to go into the final round in 27th place.
It was a near faultless display on Sunday as he racked up five birdies and an eagle as he gained 23 places on the leaderboard.
This week is the second of the WGC events.
The Cadillac Championship is once again in Florida at the TPC Blue Monster course in Doral, Miami.