Five-time Crucible champion Ronnie O'Sullivan let a 5-1 lead slip in the first session of his Betfred World Championships first round tie against Gary Wilson but is still 5-4 ahead.
The Rocket, in his 25th appearance at the Crucible, will resume his match on Sunday at 2.30pm against the 31-year-old Wilson who is making his Sheffield debut.
After storming into a 5-1 lead, O'Sullivan appeared to be cruising into the second round but the qualifier from Wallsend won four frames on the spin to set up an intriguing second session.
The Rocket scored two half-centuries to win the opening two frames, the first of which lasted 37 minutes as Wilson battled unsuccessfully to find the required snookers.
In a near-repeat, O'Sullivan again made 58 but needed a second visit, this time making 63, to finish off the third frame.
Wilson's highest break of the match thus far, 54, ensured that he went into the mid-session interval with a frame on the board as he trailed 3-1.
O'Sullivan then struck the first century of this year's Betfred World Championships as he made 122 to restore his three-frame advantage.
And the 41-year-old had to fightback with a clearance of 35 in frame six to tie the frame at 58 each before making no mistake with the respotted black after Wilson's failed attempt at the double.
Breaks of 64 and 63 though saw Wilson claw two frames back and in a topsy-turvy ninth frame it was the 31-year-old who came out victorious to set up an exciting second session on Sunday.
The winner will go on to face either 2005 world champion Shaun Murphy or Yan Bingtao who, at 17 years of age, became the first person born in this millenium to play at the home of snooker.
Watch the Snooker World Championship Live on Eurosport and Eurosport Player, with Colin Murray and analysis from Jimmy White and Neal Foulds