World number 16 Swail, who came back from the brink to beat Sean Storey and title-holder Mark Williams in his two previous matches, trails 6-2 after the first session against his practice partner.

For Wallace, it continues his dream debut in the televised stages of the sport’s most prestigious tournament and the qualifier from Dungannon is almost halfway towards an unexpected place in the last four.

Nobody could begrudge the world number 59 a semi-final berth on the way he has played at the Crucible, with only Matthew Stevens having conceded fewer frames in the opening two rounds.

And he certainly outplayed Swail when they started out on their best-of-25-frames encounter, maintaining the solid break-building play which has brought convincing victories over Alan McManus and Mark King.

It was not spectacular scoring from the 31-year-old accountancy graduate today but runs of 65, 52, 48 and 45 all proved good enough to win frames.

In contrast, Swail could manage only a 49 and a 37 in the same frame as the superb form he produced in the final session against Williams, which included the tournament’s highest break of 140, totally deserted him.

In this afternoon’s other match, John Higgins turned round a 3-1 interval deficit to win every frame after the break and lead 5-3 against Ken Doherty.

A fluke on the penultimate red allowed Doherty to clear up in the opener and after Higgins had equalised, the Irishman knocked in superb breaks of 114 and 91.

But the Scot took command after the resumption and his contributions included a 98 and a 72 as he claimed an overnight lead.

Embassy World Championships, Sheffield

Quarter-finals: (2) J Higgins (Sco) leads (7) K Doherty (Irl) 5-3. Frame scores (Higgins first): 54-67 58-47 0-114 (114 break) 0-95 72-18 70-48 99-0 62-17.