Graeme Dott came through a last-frame thriller to beat Mark Allen 13-12 and set up a World Championship semi-final with Ronnie O'Sullivan or Mark Selby.

After losing the first four frames, Dott, champion in 2006, recovered to start Wednesday at 8-8 and moved to 10-8 with breaks of 65 and 54.

Allen edged a monumental 20th and made it four in a row to sniff victory.

But the Scot hit back with a 115 and secured his third successive frame to complete a magnificent comeback.
After a titanic battle in the first two sessions seeing Dott and Allen sharing 16 frames, the champion from four years ago raced out of the blocks on Wednesday morning.

Dott, based in Larkhall, looked in flowing form and eased into a 10-8 lead only to see his opponent from Northern Ireland turn on the power and get back on level terms at 10-10.

Allen has blossomed in this tournament with comfortable wins over Tom Ford and Mark Davis, as well as a 146 break, and a combination of potting and safety helped him win an enthralling 20th frame.

The world number 11 had built up a 20-point lead and after Dott wasted several openings, Allen pounced to sneak it, with the highlight an incredible two-cushion recovery when snookered behind the blue.

Dott looked favourite in the next with a 53, but last year's Crucible semi-finalist stole it and went on to pinch his fourth frame in a row to get within one of the finish line.

Back came the 32-year-old Dott with a nerveless century to stop the rot and his surge continued to take it to a decider.

With the initiative and momentum firmly in the Scot's corner, Dott knocked in a 28 and after Allen spread the balls when snookered, the former champion held his nerve to wrap up a hard-earned win.

O'Sullivan and Selby resume their battle at 1430 BST at 4-4, but the winner will have their work cut when they face a hugely impressive Dott for a place in the weekend's final.