Lee Westwood was leading a strong European challenge as American Jimmy Walker held a narrow lead midway through the opening round of the WGC – Mexico Championship.
Walker raced to five under par but Westwood was only one back, alongside Venezuela’s Jhonattan Vegas, after turning in 33 and adding a further birdie on the first.
Meanwhile Rory McIlroy found the thin air of Mexico City to his liking as he enjoyed a solid start on his return to competitive action.
McIlroy has played just once in 2017 due to a rib injury which saw him push through the pain barrier before losing to Graeme Storm in a play-off for the South African Open hosted by the City of Ekurhuleni in January.
The 27-year-old still arrived at Chapultepec Golf Club knowing that he could reclaim top spot in the Official World Golf Ranking for the first time since August 2015 by winning his third World Golf Championships title, as long as current number one Dustin Johnson finished joint fourth or worse.
And McIlroy was in the ideal place to keep an eye on Johnson's progress over the first two days after being paired with the US Open champion and Japan's Hideki Matsuyama.
Starting on the back nine of a course which reaches a maximum of 7,800 feet above sea level, McIlroy holed from 15 feet for birdie on the par-five 11th and added seven pars in succession to reach the turn in 35.
The four-time major winner then drove into a greenside bunker on the short par-four first hole and got up and down for birdie to reach two under par, while Johnson ran up a double bogey after hitting his tee shot out of bounds.
That dropped Johnson back to level par and five behind early pacesetter Jimmy Walker, the US PGA champion enjoying a one-shot lead, with English trio Ross Fisher, Tommy Fleetwood and Chris Wood all a shot further back.
Spain's Sergio Garcia and compatriot Jon Rahm were also three under, Rahm having joined the European Tour as an affiliate member this week.
Forty-nine of the world's top 50 are in the 77-man field, with World Number Two Jason Day absent due to illness.
