Robertson was in imperious form

The Australian took a 10-6 lead into the final session which he extended to 11-6 with a 65 break.

Lee won two of the next three, but a mistake on a long red in the 22nd frame let the 24-year-old in for a 102 break.

Robertson, the first Australian to go this far since Eddie Charlton in 1983, now plays Nigel Bond or Graeme Dott.

The Australian, who beat Gerard Greene to make it to The Crucible, said he was delighted with his form after reaching the quarter-finals for the first time.

My safety was not good enough throughout and I paid the price Stephen Lee

"It was a fantastic match. The first session was the best I've ever played over a five or six-frame period," said the world number 27.

"That was a new level for me. If I can maintain that standard I can do really well here.

"It's a pretty proud moment for me and has made it a pretty handy season."

Lee believed the tactical side of his game let him down against Robertson.

"My safety was not good enough throughout and I paid the price," said the Welsh Open champion.

"You can't afford to let Neil get his hand on the table.

"I played good stuff in patches but made a mess of a few frames and he took advantage. He's a good player, better than I thought."

S Lee (Eng) 9-13 N Robertson (Aus)
53-66 24-74 0-109 (109) 72-0 (64) 135-0 (135) 0-74 (74) 1-105 (56) 7-74 (73) 78-4 61-79 (70) 68-34 58-71 1-85 76-20 49-87 120-12 (113) 0-76 (65) 73-1 0-105 (50) 110-0 (110) 70-24 8-102 (102)