Magnus Carlsen led early on before Wesley So roared back as the first day of a tense Opera Euro Rapid final ended all-square.
The pair now goes into Sunday's second day for a final-set shootout for the Meltwater Champions Chess Tour event's title.
It was a slow start yet Game 1 eventually sparked into life when Carlsen, with the White pieces, made a small mistake. It left So with the winning chances and he went for it. So got so close, but not close enough as Carlsen held on for the draw.
Game 2 started with a super-sharp line of the Two Knight Defense dangerous for both sides, and it was the champ who found himself on the wrong end of it.
But with victory in his sights, So blundered and in just one move the game turned around. Carlsen made no mistake to convert. It was a painful missed opportunity for So, but a thrilling game to watch.
Game 3 was a totally different affair. It lasted only 60 seconds as both players steered it to a super-quick draw.
For Carlsen, now 2-1 up with one to play, the strategy appeared to make sense and he said after at that point he was "knackered".
For So, however, it was a more risky idea as taking the draw meant gambling the set on winning the last game with the White pieces.
But it worked. Near the end, with Carlsen needing just a draw, the game exploded into life as So created a stunning checkmate threat. It was devastating and Carlsen had to resign.
So, speaking from his home in Minnetonka, USA, said he was "thrilled to win on-demand with the White pieces" and happy to rescue the set.
Carlsen had missed the chance to be in the driving seat in the final but was still happy with sharing the first set.
He said: "I'm fairly happy with a draw today so I will just try and push a little bit harder tomorrow."
In the match for third place, Teimour Radjabov wrestled first set from Maxime Vachier Lagrave after winning Game 4 with white pieces.
Tomorrow's grand finale resumes at 17:00.
Opera is the official browser of the Tour and title partner of the event which carries a $100,000 prize pot.
The Meltwater Champions Chess Tour, organized by the Play Magnus Group, is the first full season of top-level online chess events.
It comprises nine Regular and Major tournaments culminating in a $300,000 Final which starts in September.
All matches are played in a rapid chess format with blitz and “armageddon” tie-breaks if needed.
For further information, please contact:
Leon Watson, PR for Champions Chess Tour
+44 7786 078 770