MEXICO CITY (AFP) - Dustin Johnson captured his 20th US PGA Tour title on Sunday (Feb 24), firing a five-under par 66 to beat Rory McIlroy by five strokes in the final round of the WGC-Mexico Championship.

The 34-year-old American finished with a 21-under 263 total to win this event at the Club de Golf Chapultepec for the second time in three seasons.

McIlroy closed with a 67 thanks to a a sizzling back nine - six birdies in seven holes before a bogey at 18 - but it wasn't enough catch red-hot Johnson, who posted five of his six birdies on the back nine.

Johnson has won at least won an US PGA event in 12 consecutive years, with his 20th career win coming in his 246th start.

Englishmen Paul Casey and Ian Poulter shared third on 273, shooting 65 and 68 respectively in the fourth round, with Thailand's Kiradech Aphibarnrat, who fired 68 to join the pack 10 off Johnson's pace.

Sergio Garcia, Patrick Cantlay and Cameron Smith shot identical 70s and shared sixth. Justin Thomas had the round of the day with a nine-under 62 which left him ninth.

Johnson got off to a tentative start with a bogey on the par-3 third hole before making birdie on the par-5 sixth.

He kicked it into high gear on the back nine with back-to-back birdies on the 10th and 11th holes and then strung together three birdies in a row beginning at the par-4 14th.