Anthony McGill pegged Ronnie O’Sullivan back from 4-1 down to leave their World Championship second-round tie finely poised at 4-4 on Thursday.
It was Crossover Day in Sheffield with round two commencing, while the remaining first-round clashes played to a conclusion at the Crucible.
Reigning champion O’Sullivan resumed his title defence against world number 16 McGill, who he had beaten in all six of their previous encounters.
And the Rocket took the opening frame with a neat break of 81.
McGill, who beat Ricky Walden 10-5 in round one, responded well with runs of 52 and 79 to level.
But the six-time champion found another gear with back-to-back centuries of 105 and 138 moving him 3-1 up at the mid-session interval.
A run of 49 then did the trick in frame five after his opponent failed to convert a couple of opportunities that fell his way.
The Scotsman, who has failed to progress beyond this stage of any ranking event since reaching the semi-finals here last August, needed a response and got one.
He controlled the sixth frame to cut the gap and although he saw a 147 attempt go begging after missing the 13th black in the next, that break of 97 was more than enough for him to trail 4-3.
McGill then took the final frame of the session to square the match and set up an exciting finish on Friday.
Elsewhere, Neil Robertson established a 5-3 overnight advantage against fellow left-hander Jack Lisowski.
Both players struggled to settle into their natural rhythm early on and a scrappy opening two frames were shared.
Lisowski suffered a humbling 13-1 drubbing at the hands of John Higgins on his only previous second-round appearance in 2018.
But the world number 14 averted that this time around as he won two of the next three frames, with breaks of 85 and 81 putting him 3-2 up.
However world number three Robertson, who has won all five previous meetings between the players, levelled once more, before finishing with a flourish.
A superb total clearance of 135 edged the UK and Tour Championship winner ahead, before a run of 76 gave him a two-frame buffer at the close of play.
Meanwhile, Mark Selby completed the second-round line-up after sealing a comprehensive 10-1 rout of Kurt Maflin.
Holding a commanding 8-1 overnight lead, the three-time World champion wasted no time in getting the job done and setting up a showdown with Mark Allen.
“The first round is always tough for me – especially mentally. You always go out there a little bit nervous,” Selby told Eurosport.
“When the draw came out, there aren’t many players tougher than Kurt. He came here last year and had a great tournament, so I knew I had to be on my game. Thankfully for me, I was.
“I played Kurt the year I was defending champion in 2015. I played quite well against him and went 8-4 up, then the next minute, I’m 9-8 down and he should’ve beaten me 10-8.
“I knew it was going to be a tough game. I’m happy with the win, but even more pleased with the way I played.”
Earlier, Shaun Murphy also booked his place in round two with a 10-7 success over Mark Davis.
The 2005 champion, who had lost in the first round three times since reaching his third Crucible final in 2015, trailed the Hastings qualifier 5-4 heading into the concluding session.
But he won four of the first five frames – hitting breaks of 56 and 93 along the way – to pull two clear at 8-6.
Making his 12th Crucible appearance – and 11th as a qualifier – Davis stopped the rot in the next, but it proved a false dawn as the Magician quickly regained control before producing a magnificent 131 total clearance to secure a second-round date with Masters champion Yan Bingtao.
World Snooker Championship 2021 Scores
Thursday April 22
Shaun Murphy 10-7 Mark Davis (R1)
Mark Selby 10-1 Kurt Maflin (R1)
Ronnie O’Sullivan 4-4 Anthony McGill (R2)
Neil Robertson 5-3 Jack Lisowski (R2)