Wu Yize and Mark Allen’s semi-final is poised at seven frames all after their afternoon session ended with a bizarre frame – the longest in the World Snooker Championship’s Crucible era – clocking in at just over 100 minutes.

Allen began the afternoon trailing 6-2 overnight to an opponent high on confidence and belief, but fought back in style, winning five frames in succession to edge 7-6 ahead.

The session at the Crucible concluded with a remarkable 14th frame, with a cluster of eight reds jammed around the black ball on the edge of a corner pocket. It resulted in a lengthy stalemate, 55 minutes passing without a ball being potted.

Allen led the frame 47-13 and so did not want a re-rack. The referee, Marcel Eckardt, struggled to control the crowd after some spectators began slow clapping. But he seemed hesitant to act, and did so only after being prompted by the tournament director, Rob Spencer, who instructed Eckardt to tell the players they had three shots to resolve the situation or there would be a re-rack.

Allen was forced to commit a foul by knocking the black into the pocket, which enabled Wu to move ahead in the frame, eventually winning it 88-66 after a lengthy safety exchange and an excellent escape to hit the pink ball from in behind the black.

The gruelling frame was finally completed in one hour, 40 minutes and 21 seconds – the longest in history, and just eight minutes shorter than the Crucible’s quickest match. That came in 2020, when Ronnie O’Sullivan defeated Thepchaiya Un-Nooh 10-1 in 108 minutes.

Steve Davis, six times the world champion, told BBC Sport: “In a nutshell, that frame is an embarrassment to snooker, and the referees and players’ association need to try to work out a way that never happens again.”

The seven-time winner Stephen Hendry called for the German official to end the stalemate much earlier, saying: “The referee’s got to get involved here, in my opinion. This is the dark side of snooker.”

Kyren Wilson, the 2024 champion, said: “I think Marcel Eckardt should’ve called that a lot earlier. That game was going nowhere, quite painful, but the fight and determination from Mark Allen is still incredible.”

The Northern Irishman had dug deep to win the first two frames of the afternoon, despite Wu making breaks of 32 and 51, and Allen needing snookers in the second. He followed that up with a tournament-best 145 break, then claimed another scrappy frame to go into the mid-session interval level at 6-6.

Allen maintained his momentum after the interval to go ahead with a 121 break, his ninth century of the tournament taking him one clear of Zhao Xintong as the tournament’s top break-builder. Three further frames were expected, but the extraordinary attritional battle of the 14th frame meant the session ended at 7-7.

John Higgins moved into a 13-11 lead over Shaun Murphy as their tight tussle continued on Friday evening. They went into the session tied at 8-8 and little separated them in an entertaining battle.

Murphy started the evening session with a break of 60 to clinch the opening frame but Higgins replied with a run of 55. Some mistakes in the following frame resulted in a close scoreline before Higgins took advantage and potted the brown, blue and pink in quick succession to take a one-frame lead. But Murphy responded with a commanding display to win the next, hitting a comfortable 82 break to draw level again at 10-10 at the mid-session interval.

After the restart, Higgins looked to have allowed Murphy back in, but the Scot’s early break of 63 underpinned the frame as he potted the pink to win.

Murphy again levelled with one visit to the table, hitting a 105 break to become the fifth player to reach 100 century breaks at the Crucible. Higgins then took control towards the end of the session, winning back-to-back frames including a 101 break in the final one to hold a slender overnight advantage.