Two-time Embassy world champion Mark Williams, snatched a slender 5-3 advantage over Preston's Ian McCulloch with a cool display of potting in their entertaining second-round clash at The Crucible.

Gwent star Williams, from Cwm, winner of the world crown in 2000 and 2003, compiled two century breaks - 133 and 102 respectively - to give the Lancashire left-hander plenty to think about.

It was an excellent long pot in a black ball-decided final frame of the session which saw Williams earn himself a welcome two-frame cushion.

Having missed a routine red into the middle on a break of 62, Williams was given a reprieve when McCulloch, himself on a break of 36, ran out of position on the black he needed to secure a 4-4 scoreline.

That error proved costly and after a couple of safety exchanges, Williams, full of confidence after his memorable 147 maximum earlier in the week, held his nerve to sink the black and deny McCulloch the chance to level.

McCulloch admitted afterwards he was happy with a 5-3 scoreline, although to have finished at 4-4 would have been a "real bonus" in the circumstances.

The Englishman started the better and despite Williams opening his account with a 59 break, he won the first frame of the pair's best-of-25 match on a re-spotted black.

Williams hit back with a magnificent 133, before McCulloch restored his lead with a break of 60.

But Cardiff-based Williams, also a beaten finalist in 1999, replied in style to win the next three frames.

In the fifth he grabbed his second century of the match (102) and then had breaks of 49 and 60 to edge 4-2 ahead.

McCulloch hit back with a 90 break, but squandered his chance to share the spoils and Williams made no mistake with the long black he needed to edge closer to a place in the quarter-finals.