Cahill, the first amateur to play at the World Championship, leads Ronnie O’Sullivan 5-4 at the halfway stage of their first-round match in Sheffield.
World No 1 O’Sullivan looked out of sorts throughout and must pick his game up when play resumes this morning.
Cahill rarely looked in awe of his fancied opponent, who is chasing a sixth world crown.
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.
Higgins had lost six of the previous seven meetings with Davis, from Sussex. He had also suffered heartbreak in the 2017 and 2018 finals and has struggled to find motivation since.
Higgins began the afternoon session with a healthy lead, ahead 6-3. However, breaks of 57 and 64 helped Davis to immediately close the gap to 6-5. Higgins went into the mid-session break with only one frame to his name, leading 7-6.
But he moved to the verge of victory with two century breaks, of 135 and 132, and he clinched the tie in the 17th frame, to book a second-round meeting with either Stuart Bingham or Graeme Dott.
He said: “I’d like Graeme to win because he’s one of my mates on the tour and a fellow Scotsman. That would be a great occasion. Stuart has been one of the players of the season.
“People are saying our half of the draw is pretty easy, but there are four world champions and that’s not counting Barry Hawkins and Kyren Wilson. There’s never an easy draw, and there’s always shocks aplenty here.”
In the morning session, three-time champion Mark Selby had to fight back in the opening instalment of his first-round clash, recovering from 5-1 down against Zhao Xintong to close out at 5-3.
The Leicester man is desperate to find some form in Sheffield, having made first-round exits in the same tournament last year, this season’s UK Championship and at other notable events during the campaign, including last month’s Players Championship.
While Selby was toiling, Shaun Murphy, left, was condemning Luo Honghao to the heaviest defeat in tournament history.
In winning 10-0, Murphy became only 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 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 told 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.”