Stevens beat world number one Mark Williams 5-1

Williams made a break of 54 to win the first frame but Stevens went on to reach his first ranking-event semi-final since the 2002 Thailand Masters.

He said: "It's an excellent result to beat Mark, a great scalp for me."

Williams admitted: "He outplayed me and I fancy him to go on and win the tournament now."

He added: "It's nice to see him back playing some good stuff. He's proved you don't have to play frame-winning breaks all the time, you just have to be solid, play good safety and take your chances."

Stevens will play three-time winner Stephen Hendry, who beat fellow Scot John Higgins 5-4.

Hendry looked certain to win 5-3, but missed a simple red in the eighth frame and Higgins forced the contest its full distance.

And Higgins, the runner-up in last month's LG Cup, had the first chance in the decider, but went in-off on 12 and a relieved Hendry pieced together a break of 71 to secure his semi-final place.

"I was fortunate to get a chance in the decider after missing a really good opportunity to win the match," Hendry admitted.

"It was a twitch on the red, but I ended up taking my chance well."

The defeat left Higgins feeling bitterly disappointed.

"I'm really gutted to lose - at 3-1 up, I was in control, but I missed too many balls after the interval. It's really disappointing."

Ronnie O'Sullivan ground his way to a 5-4 victory over Gerard Greene.

O'Sullivan looked to be on his way out against the world number 38, but Greene fouled with just the colours left at 4-4 to hand his opponent victory. "I'd have rather have gone through by potting a good ball," said O'Sullivan, the world number three.

"It was looking dodgy. The crowd were getting behind Gerard and he was growing in confidence. I had to concentrate on my own game.

"The only way I was going to win was by staying strong in myself, which is what I did."

O'Sullivan will face Stephen Lee, who beat defending champion Paul Hunter 5-3.

Lee admitted he had done his best to prevent Hunter from getting many scoring opportunities.

He said: "Paul is a very tough player. You can thump him and thump him and he still gets up.

"If he gets his confidence going he'll pull away from you so I just didn't want to leave him in."