With the chasing pack gathering, the first test for Shubhankar Sharma came on the first hole of his third round at the WGC Mexico Championship.
Now the 21-year-old from India has one last round to hold off a few of golf's biggest names.
The Club de Golf Chapultepec features a drivable par 4 to start, but the par-4 second, although not long by today's standards, was not created to be reached in one shot.
This meant he had to close with a brilliant par save at the last as he calmly rolled in a 15-foot putt to maintain his lead.
Sharma was at 13-under 200.More news: Winter storm kills five people, leaves millions without power in United States
That left him 18 holes away from capping off his unbelievable rise.
Phil Mickelson played bogey-free for a 65 that will put him in the last group with Sharma and England's Tyrrell Hatton, who had a 64. At 11-under, he was two shots ahead of reigning Masters champion, Sergio Garcia, 2017 PGA Tour Rookie of the Year Xander Schauffele and Spaniard Rafa Cabrera Bello.
Top-ranked defending champion Dustin Johnson eagled from 112 yards at the par-4 ninth, landing the ball beyond the hole with a 60-degree wedge and back-spinning it into the cup.
"It's been a long time since my game's been back to this point", Mickelson said.
"I'm putting the ball in play better, my iron play's back, my short game is back, I've been putting well, so overall I've been playing well and the scores are starting to reflect it", said Mickelson, who won this event (2009 at Doral) during a different era. I just got off to a great start. Now 21, Sharma has put his career on course with two massive wins-the Maybank Championship and the Joburg Open-in 2018.More news: Top four scrap will boil down to survival of the fittest
"I think whether it happens tomorrow or not - very good chance it will - but if it doesn't, it's going to happen soon because I'm playing too well for it not to". Spieth birdied three of his last four holes and was six behind.
In his first appearance in a World Golf Championships event, Shubhankar added a five-under-par 66 to his opening round 65 to set the pace at 11-under 131 at Club de Golf Chapultepec.
Despite recent victories in South Africa and Malaysia, and leading the European Tour's Race to Dubai standings, Sharma has yet to qualify for the first major of the year.
He rolled in a 16-foot birdie putt at 14 to reclaim sole possession of the lead, and he was two clear even after his bogey at 16. "Really happy with the way I played today, stuck in there", said Sharma, who is making his debut appearance in the World Golf Championships.More news: There are five types of diabetes not two, say scientists