Mark Selby dodged a fist bump with Ronnie O'Sullivan before edging out his rival to secure a place in the semi-finals of the 19.com Scottish Open in Glasgow.
The pair had exchanged a humorous 'rock, paper, scissors' greeting before Friday's quarter-final.
The sporting gesture followed on from O'Sullivan's fist bump, rather than a traditional handshake, with James Cahill and the referee ahead of their second-round contest because he was "a bit OCD with germs".
👊 Rock🖐 Paper ✌️ Scissors@markjesterselby isn't having @ronnieo147's pre-match fist bump 🤜🤛 🔴 Watch O'Sullivan v Selby at the #ScottishOpen LIVE📺 Eurosport 1📺 @QuestTV📱💻🖥 Eurosport Player: https://t.co/0Fa7uXMVB9 pic.twitter.com/Dbkv7zSGw0 — Eurosport UK (@Eurosport_UK) December 13, 2019
There was, though, no shortage of clinical action on the table, as both players chalked up centuries during the opening four frames, which were shared.
O'Sullivan then pushed in front with a 111 clearance, but Selby mounted a recovery to force a decider, which he clinched with a break of 63.
"Every time I play Ronnie, I always see myself as the underdog, irrelevant of what I have won in the game," three-time world champion Selby told Eurosport.
"I think that is the same for everyone else. In my eyes, he is the best player to have played the game.
Mark Selby beats Ronnie O'Sullivan to book his semi-final spot. 5-4 in a dramatic finish. Rocket. Paper. Scissors. #ScottishOpen pic.twitter.com/8T9eB7KckR — World Snooker (@WorldSnooker) December 13, 2019
"I am not sure about his fist bumps and all that, but as far as on the table, he is a great, great player."
Afterwards, O'Sullivan paid tribute to Selby's resilience.
"Mark played well, he played good stuff, good safety and a brilliant break at the end under pressure. That's what champions are made of," O'Sullivan said.
"I'm happy with my performance this week. Mark's a brilliant match player. I think I've done alright, I'm happy to be able to compete."
Earlier on Friday, defending champion Mark Allen saw off Scott Donaldson 5-1, having returned to the table following his late-night victory over Chris Wakelin.
"The schedule this week has been disgraceful when it comes to my matches," the Northern Irishman said.
"Being defending champ, I knew I'd start off on Monday. Then I was 10am Wednesday, 10am Thursday, then last on at night and then first on Friday.
"Some very strange decisions, but no one wants to take the blame for it."
David Gilbert knocks out Judd Trump to set up a semi-final clash with Mark Selby tomorrow. A break of 142 the pick of the bunch. #ScottishOpen pic.twitter.com/cRbmpwu57i — World Snooker (@WorldSnooker) December 13, 2019
Friday's late matches saw world number one Judd Trump suffer an unexpected 5-2 defeat against David Gilbert, who produced a 142 clearance in the sixth frame.
Jack Lisowski defeated Thailand's Thepchaiya Un-Nooh 5-3 to book a semi-final against Allen.
The world number 14 had made the tournament's highest break of 143 in the third frame.
