|WGC-Mexico Championship first-round leaderboard|
|-6 R McIlroy (NI); -4 B Watson (US), J Thomas (US); -3 L Oosthuizen (SA), B Horschel (US), C Conners (Can), B DeChambeau (US)|
|Selected others: -2 T Hatton (Eng), P Casey (Eng), L Westwood (Eng), P Reed (US); -1 T Fleetwood (Eng); +1 M Fitzpatrick (Eng); +5 G McDowell (NI), D Johnson (US)|
World number one Rory McIlroy carded a six-under-par 65 to take a two-shot lead after the opening round of the WGC-Mexico Championship.
The Northern Irishman, 30, runner-up to Dustin Johnson last year, began from the 10th and eagled his second hole, before three birdies in his last four.
American left-hander Bubba Watson had a career-best 21 putts and shares second with world number four Justin Thomas.
Johnson, however, ran up four bogeys and a double bogey in a five-over 76.
McIlroy, who won the WGC-HSBC Champions in Shanghai in November for his 18th PGA title, hit some typically enormous drives and sparkling iron shots, but also sank some long putts at the Club de Golf Chapultepec.
On the 520-yard par-four eighth he hit a drive and eight iron and holed from the back of the green, before a wedge to nine feet at the last set up his fifth birdie of the day.
"All aspects of my game were working well, the big thing was I putted well," said McIlroy, who reverted back to a former putter having experimented with a new one last week at the Genesis Invitational, when he slipped to a 73 in the final round and finished fifth.
England's Paul Casey drove the green to eagle the the 303-yard first - his 10th - and is two under alongside compatriots Tyrrell Hatton and Lee Westwood.