Mark Allen takes the lead in World Snooker Championship semi-final against Mark Selby

A 123 clearance gave Selby the ideal start but uncharacteristic errors in the safety battles in the next two frames allowed his Northern Irish opponent to take control with breaks of 63 and 66.

Selby missed a black off its spot in the fourth frame but still went into the mid-session interval level at 2-2 as it was Allen’s turn to fluff his lines in a tactical exchange.

A break of 68 moved Selby into the lead in an ebb-and-flow session and while Allen levelled, there was a hint of controversy when replays showed he grazed the red he was bridging over to make a tough pot.

The referee did not spot the foul while Allen did not acknowledge it either so – with players so scrupulous in calling to attention any wrongdoing when they are at the table – the suggestion was the left-hander, who has won three ranking events this season, was oblivious to what he had done.

Selby did have a visit to the table thereafter but his rival’s break of 64 left him well adrift and Allen quickly wrapped up the frame. Allen then finished the session with breaks of 60 and 78 to seize the initiative.