Amateur James Cahill is five frames away from producing one of the all-time sporting shocks at the Crucible.
The first amateur to play at the World Championship, Cahill leads Ronnie O'Sullivan 5-4 at the halfway stage of their first-round match in Sheffield.
O'Sullivan, the world number one and near-unbackable favourite, looked out of sorts throughout and must pick his game up when play resumes on Tuesday morning.
Cahill rarely looked in awe of his fancied opponent, who is chasing a sixth world crown.
Three-time champion Mark Selby hit back from 5-1 down in the morning session to finally triumph 10-7 against Zhao Xintong.
The Jester from Leicester had battled back to be 5-3 down and continued to recover, eventually hitting three century breaks and five over 50 in his victory.
Selby avoided another first-round exit in Sheffield having also bowed out early at the UK Championship and at other notable events during the campaign, including last month's Players Championship.
While Selby was toiling, 2005 champion Shaun Murphy was condemning Luo Honghao to the heaviest defeat in tournament history.
In winning 10-0, Murphy became just the second man to record a Crucible whitewash, while Luo's 89 points were a record low.
Murphy now faces Neil Robertson, who won his first-round clash against Michael Georgiou 10-1, and hopes he can make the most of his late-season form.
"After the season I have had, never in my wildest dreams did I think I could come here and win 10-0," Murphy is quoted as saying by World Snooker's official website.
"Going out this morning, it was tough to try to put that potential 10-0 to the back of my mind and try to play the right shots.
"This has been the worst season of my life, I have been in a daze. Yesterday I felt like Shaun Murphy again. In a way I'm looking forward to this season being over, but while I'm here I'll give it my best."
John Higgins, hunting a fifth title, is safely through to round two after beating Mark Davis 10-7, rattling in breaks of 100, 135 and 132 along the way.