Ronnie O'Sullivan is more than halfway towards claiming his first Embassy World Championship title after overcoming a mid-match blip to lead Scotland's John Higgins 10-6 in the final at Sheffield.

For just about the first time in the past fortnight, O'Sullivan let his exceptionally high standards slip in the opening four frames of the second session.

His 6-2 lead from the first session was reduced to 7-5 as he started missing pots he had been converting with relentless accuracy and giving a tired looking Higgins the chance to get back into the match.

But normal service was resumed after the interval as two breaks of 99, plus a century ensured the "Rocket" holds a four-frame advantage going into the final two sessions today.

Now the 25-year-old only requires eight of the remaining 19 frames to make sure of snooker's most coveted crown.

Higgins had been involved in a gruelling semi-final with Matthew Stevens until late on Saturday evening which looked to have taken its toll.

Higgins, the 1998 world champion, is a resourceful and determined character capable of launching a revival and he has the total respect of O'Sullivan.

But it is difficult to see O'Sullivan, the youngest winner of a ranking tournament eight years ago at just 17, being denied if he can hold himself together for just one more day.

It was crucial for Higgins to make quick inroads into O'Sullivan's lead after the afternoon session and he made a confidence-boosting start with a 60 break.

He then inadvertently pushed all the remaining reds into pottable positions to give O'Sullivan the opportunity to force a re-spotted black.

After reducing his leeway to 49-67, O'Sullivan broke down on the blue and a relieved Higgins was able to make sure of the frame.

The 10th was a scrappy low-scoring affair and this time Higgins conceded after missing the final blue.

A run of 37 helped him to win the next and, after O'Sullivan had put together a 45 in the 12th, Higgins responded with a 35 clearance to the pink to go into the interval only 7-5 in arrears.

But any temporary loss of form was soon put behind O'Sullivan when he came back into the arena for the final four frames of the day.

There were brief visions of an O'Sullivan maximum break in frame 13 with the reds all perfectly placed.

He took six blacks, but then, clearly more concerned with making sure of the frame, opted for the blue and a 99 break extended his lead.

O'Sullivan went one better in the next with a 100 clearance to take him halfway towards his 18 frame target to become crowned world champion.

Higgins responded with a 107 clearance to give his supporters renewed hope, but O'Sullivan re-established his four-frame advantage with another 99.

Higgins had been made slight favourite by the bookmakers at 8 to 11 at the start of the final despite his sapping semi-final with Stevens plus O'Sullivan's brilliant form in the tournament.

On Saturday, O'Sullivan had completed his expected semi-final victory 17-11 over Joe Swail, who has yet to reach the final of a ranking tournament.

Swail believes that O'Sullivan is playing well enough to secure his first world title after tasting defeat in the semi-final for the second successive year.

"He is definitely playing well enough to win it. I'll be very surprised if he doesn't manage that," said Swail. "He will have a tough final but his game is spot-on, a joy to watch. He is an absolute genius. Peter Ebdon was right when he compared him to Mozart."

Swail admitted: "I can't really say I enjoyed it because I did feel an awful lot of pressure. I was desperate to get into my first final. I honestly felt that this was my year.

"But I let Ronnie get off to a good start and he is the type of player who will not let you get back at him."