Rory McIlroy's overnight lead disappeared in the space of three holes as Dustin Johnson signalled his intent to remain World Number One at the WGC-Mexico Championship.
McIlroy's only previous appearance in 2017 had come in the South African Open hosted by the City of Ekurhuleni in January, when he lost out to Graeme Storm in a play-off despite suffering from what was subsequently diagnosed as a stress fracture to his ribs.
The 27 year old still arrived in Mexico City knowing that he could reclaim top spot in the Official World Golf Ranking for the first time since August 2015 by winning his third WGC title, as long as current number one Johnson finished worse than outright fourth.
And McIlroy looked ideally placed to deliver on his part of the bargain after a second round of 65 at Chapultepec Golf Club left him two shots ahead of Phil Mickelson, Justin Thomas and Ross Fisher, with Johnson a shot further back.
However, Johnson was not about to give up the coveted number one ranking without a fight and make a spectacular start to the third round, reaching the green on the short opening hole with a long iron and holing from 20 feet for an eagle.
The US Open champion then birdied the second from a similar distance and holed from even further to save par on the third, following a clumsy chip from the back of the green.
McIlroy got up and down from a greenside bunker on the first to regain the outright lead, only to bogey the next after a wayward tee shot meant he could only pitch out sideways from the trees.
And when he also bogeyed the third, the four-time Major winner found himself a shot behind Johnson and Mickelson, who had chipped in for a birdie on the first and picked up another shot after chipping in on the fourth.
