Wu Yize and Mark Allen’s semi-final is poised at seven frames all after their afternoon session ended with the longest frame in World Snooker Championship history, 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 a row to edge 7-6 ahead.

The session at the Crucible Theatre concluded with a bizarre 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, making it difficult for the referee, Marcel Eckardt, to call for a re-rack. Eckardt asked the crowd to settle after some spectators began slow clapping, and warned the Northern Irishman that the impasse could not go on forever.

After Allen committed a foul by knocking the black into the pocket, Wu was able 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 World Championship 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.

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.

Steve Davis, a six-times 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.”

Earlier, Shaun Murphy battled back to leave his semi-final against John Higgins finely poised at 8-8 before their evening session in Sheffield.

The standard of play was a sizeable upgrade on Thursday’s scrappy first session that was shared 4-4. But both players still wasted big opportunities to open up a commanding lead in their best-of-33 battle.

Higgins, who was won four world titles, looked as if he might be capable of achieving that advantage after taking an 8-6 lead and putting his opponent’s cueing under pressure. But Murphy, the 2005 champion, held his nerve to draw level and restore parity in a session where he had made only one break over 50.

The Englishman was in pole position to win the opening frame before his run of 49 ended when he missed a straightforward black as he attempted to cannon a red and keep position.

Higgins made a 72 clearance to lead for the first time but Murphy kept his focus in the next frame with a fine response of 88. A brilliant long red got Higgins going again and he had reached 67 before striking a frame-winning black too hard. The Scot was back in front though as a Murphy miscue let him finish matters off.

Murphy tied the scores at 6-6 after a break of 47 put him in command. Higgins failed to cut a difficult black into the corner and Murphy capitalised to reach the mid-session interlude with a spring in his step. That bounce quickly disappeared as Higgins made a decisive 57 break and Murphy lost position and momentum with a freak screw back into baulk in the next frame.

Higgins punished him with a break of 86 – his best of the match – before Murphy edged a nervy 15th frame which lasted 37 minutes. The Englishman was 53 ahead with 51 remaining and Higgins needing one snooker, which he got when Murphy found himself tucked behind the black and slid past a red up the table.

There were more safety exchanges with various colours tied up and Murphy, having potted a wonderful long green to leave Higgins requiring another snooker, could not breathe easily until sinking the pink.

Murphy was vulnerable in the final frame after a missed pink into the middle pocket ended his flow at 28. But Higgins missed a red with the rest and a double kiss cost him dear as Murphy made a 31 clearance to leave the contest on a knife edge.