Rory McIlroy's overnight lead disappeared in the space of three holes as Dustin Johnson signalled his intent to remain world number one in the WGC-Mexico Championship.
McIlroy's only previous appearance in 2017 had come in the South African Open 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 world rankings 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.
Johnson doubled his lead after a brilliant approach left him with a tap-in birdie on the sixth, but McIlroy also birdied the only par five on the front nine from short range.
McIlroy dropped his third shot of the day after coming up short of the green on the tough eighth, but made amends by holing from 20 feet for birdie on the ninth.
Playing partner Mickelson also birdied the ninth to join McIlroy on nine under par, a shot behind Johnson.
Two-time major winner Jordan Spieth carded a course-record 63 to finish seven under par, but it was his good friend Justin Thomas who moved into a share of the lead in spectacular fashion.
After birdies on the 10th and 12th, Thomas fired a hole-in-one from 232 yards on the 13th, his tee shot pitching around 15 feet from the flag and taking a big bounce before plummeting straight into the hole.
That took Thomas alongside Johnson on 11 under par, with McIlroy a shot behind after a superb pitch set up a tap-in birdie on the 11th.
Asked about the improvement in his score after opening rounds of 71 and 72, Spieth told Sky Sports: "I didn't hit any foul balls.
"I hit a couple of foul balls the first two days, a couple out of bounds, a couple unplayable. I kept it a little straighter today and just stayed aggressive.
"I think the more rounds you play out here the more you can get dialled in to trusting your numbers at this altitude. We hit quite a few shots really close to the hole today and I didn't have to work too much with the putter to get to 63."