Stephen Hendry criticised Mark Selby and Mark Allen for casting a “dark cloud” over the Crucible after the second session of their World Championship semi-final was halted three frames earlier than scheduled in Sheffield.

Selby battled back from a three-frame deficit to establish a 7-6 overnight advantage against his opponent after a gruelling session in which safety play prevailed and both players appeared reluctant to take on important pots.

Seven-time world champion Hendry, who was on punditry duty for the BBC, said: “A dark cloud came over the match table at the Crucible.

“It was not pretty. It’s not the snooker that I want to watch, but I understand that snooker has to be played in different ways. It’s almost like they’re trying to be too precise, too exact in their matchplay. Just play the ball sometimes.”

In complete contrast, Hendry had earlier been purring over the style of China’s Si Jiahui, who hit his third century of the match and five more breaks of 50-plus as he extended his lead over Luca Brecel to 11-5 ahead of Friday evening’s resumption.

Selby’s clash with Allen, who has been criticised for his slow play this season despite lifting three titles, was always going to be more attritional, and it took a superb pink from the latter to finally clinch a 45-minute opening frame.

That took Allen three frames clear at 6-3 but the Northern Irishman missed a golden chance to extend his lead, with out-of-sorts Selby dredging deep to claim the snooker he required before nervelessly clearing to reduce the deficit.

The four-time champion built on his reprieve as he recovered from 33 points down to take the 11th frame with a brilliant 95 clearance, and Allen paid for two more missed opportunities in the next as Selby duly levelled.

Another marathon frame went Selby’s way before the duo shook hands and went off to prepare ahead of their scheduled return on Saturday morning and what promises to be a long-drawn out concluding session on Saturday evening.

The first semi-final could hardly have presented a greater contrast as Si, ranked 80 in the world, stormed closer to becoming the youngest Crucible finalist in history and also the first debutant to win the tournament since Terry Griffiths in 1979.

His stunning pot success impressed former world champion Dennis Taylor who told the BBC: “I’ve been coming to the Crucible since 1977 and I’ve enjoyed watching this young player as much as anyone I’ve ever seen here.”

Showing no sign of nerves, Si got off to a quick start with a break of 64 before fluking a snooker by easing the white into the jaws of the top right pocket.

After failing to extricate himself, Brecel showed his frustration by slamming the white off the table, incurring a warning from referee Rob Spencer, but responded with a 65 to reduce Si’s lead.

A remarkable long blue was the highlight of a 122 break from Si in the following frame, and further back-to-back breaks of 89 and 58 moved the Chinese player five frames clear at 9-4.

Brecel, who was not doing a lot wrong, won the 14th frame in two visits but the irrepressible Si maintained his astonishing long-pot success rate as breaks of 55 and 71 moved him within sight of a place in the final.