Selby had ground down his opponent in overhauling his early advantage – he has won the five frames that crept over the half-hour mark – but there was little of that when Ding managed to put a break together when he got to the table.

Indeed trailing 12-10, with just two frames remaining, Ding showed extraordinary resolve in rattling off two century breaks (117 and 128) to level the match and set up a mouth-watering final session on Saturday.

It had been a very different story in their first session on Friday as Selby won six of the eight frames on offer in their morning session. Selby, who also won the world title in 2014, was unapologetic about his laborious play.

Marco Fu swept aside by defending champion Mark Selby in world last eight

“You know in this tournament you’re not going to be able to play well in every single session, it’s more or less impossible,” Selby said. “So you need to be able to scrap it out and I’ve shown in the past I can do that.”

In the other semi-final, Scotland’s four-time world champion John Higgins – appearing in his first semi-final since the last time he won the crown in 2011 – retained control advancing to a 10-6 lead after being up 5-3 overnight against Barry Hawkins.

Their last-four clash resumes on Saturday and Higgins is clearly feeling that 38-year-old Hawkins, who has reached the semi-finals in four of the last five editions, has a lot left in reserve.

Marco Fu in trouble at snooker world championship but Ding Junhui eyes semi-final after dominating Ronnie O’Sullivan

“I know how difficult Barry is to beat,” said Higgins. “In the last two or three years he’s grown into being a great champion. He always had the game but I don’t think he had the belief.

“He’s definitely got the belief now. I was saying before this event he was my pick to win it. I hope he’s not ready to win it, obviously, but he was my pick.”