John Higgins made only the 11th 147 break at the World Championship as he battled to book his place in the quarter-finals.
The 2019 finalist, who trailed Kurt Maflin 5-3 overnight, was 7-4 down when he made the maximum and ended the morning session level at 8-8.
But despite going on to nudge his way into an 11-10 lead, Higgins was hauled back by a Maflin clearance of 80 with both players looking to clinch the best-of-25 frame clash.
Maflin had won two consecutive frames in the morning before four-time champion Higgins hit back in the final frame before the mid-session interval with a sparkling maximum, the first achieved at the Sheffield venue since Stephen Hendry in 2012.
It was the 10th 147 the Scot had made in his career and in the next frame he made the most of a missed red by Maflin on a 57 break to close the gap to one.
Maflin, ranked 43 in the world and making only his second appearance in the World Championship, continued to play at a high level though.
He made no such mistake next time with a break of 81 to regain his two-frame lead before Higgins finished an excellent session in style.
He won the final two frames, the latter after his opponent could not close out a 52 break, to draw level at 8-8 at the end of the morning session.
Maflin seized the initiative when play resumed by winning two consecutive frames to move 10-8 in front, but an under-hit red to the middle let in Higgins to clear with a break of 78 then take the next two frames to move ahead.
But just when it looked like the veteran Scot would move on to seal his place in the last eight, a simple missed brown in the next ultimately allowed Maflin to clear and pull level again.
On the other table Noppon Saengkham was keeping in touch with former champion Mark Selby and the Thai held a slender 8-7 advantage with one frame of their evening session remaining.