Lee Westwood and Ross Fisher earned a share of the lead as Rory McIlroy enjoyed a positive first round in six weeks on day one of the WGC-Mexico Championship.
Westwood looked poised to claim the outright lead but was left to rue bogeys at his last two holes as he carded a 68 to join Fisher, Jimmy Walker, Jon Rahm, Phil Mickelson and Ryan Moore at the top of the leaderboard on four under par.
McIlroy defied a stomach virus to open with a solid 69, a score matched by his Ryder Cup team-mates Sergio Garcia, Chris Wood and Thomas Pieters, while new world No 1 Dustin Johnson returned an erratic 70.
Fisher set the early clubhouse target when he rolled in a 25-foot putt on the final green for his fifth birdie of the day which left him two behind Jimmy Walker, although the PGA champion followed four birdies in six holes with bogeys at two of his last three.
The in-form Rahm, who announced on Wednesday that he would be joining the European Tour in a bid to make the Ryder Cup team, also had five birdies in his confident opener, and Mickelson made it a four-way tie at the top when he emulated Fisher’s birdie at the 18th.
Westwood started at the 10th and suddenly raced into the lead with a superb mid-round birdie blitz, picking up six birdies in eight holes around the turn before giving one back when he three-putted from 60 feet at the fifth.
The veteran missed a great chance at the long next before atoning at the par-three seventh, where he knocked a sublime 205-yard iron to four feet and converted to get back to six under.
But Westwood pulled his drive into trouble at the eighth and missed an eight-foot putt for par, and he went long and left into sand with his approach to the ninth green and could not get up and down.
The leaders are one stroke ahead of McIlroy, who showed no ill-effects in his first appearance since suffering a rib injury at the BMW SA Open in January although he admitted he was not feeling 100 per cent due to a stomach complaint.
McIlroy got up and running with a 15-foot putt for birdie at the 11th, which he followed with seven straight pars before breaking the run with a good up-and-down from sand at the first.
The world No 3 dropped a shot when he three-putted from distance at the fifth, but he produced an immediate response as he drained a 30-foot putt for eagle at the next.
McIlroy missed further good chances as he parred in to remain on three under alongside Garcia, Wood and Pieters as well as American veterans Matt Kuchar and Pat Perez, with Maybank Championship winner Fabrizio Zanotti making up the seven-way share of seventh.
Last week’s Honda Classic champion Rickie Fowler fired a solid 69 to join England’s Tommy Fleetwood and rising American talent Justin Thomas on two under, with Johnson a shot further back after he offset six birdies with three bogeys and a double-bogey at the first thanks to a wild tee shot into the unknown.
Emerging English youngster Tyrrell Hatton, who enjoyed an excellent week at PGA National, did well to birdie three of the last seven holes to salvage a 70, while experienced compatriot Justin Rose also broke par.
But defending champion Adam Scott made only one par on a rollercoaster back nine and bogeyed the final two holes in a wayward 73, while Masters champion Danny Willett dropped five shots in a torrid seven-hole run to slump to a 76.
Meanwhile, Henrik Stenson will play no further part in the first WGC event of the season after he was forced to withdraw after 11 holes due to illness.