During the morning session, Welshman Williams, a three-time champion, was pushed hard by another former winner, England's Stuart Bingham, before prevailing 13-11.

Resuming at 8-8 heading into the final session, the pair shared the first four frames to go to the mid-session interval tied at 10-10.

Williams took the lead again before Bingham edged a tight 22nd frame on the pink to draw level once more at 11-11.

Bingham was ahead in frame 23 but after missing a red Williams cleared up to go one away from victory.

Williams took the lead in frame 24 with a break of 75 and despite Bingham battling for snookers, the Welshman hung on to secure the win.

During the afternoon session, another three-time world champion was pushed all the way before progressing, with England's Mark Selby overcoming Thailand's Noppon Saengkham in a decider as he won 13-12.

Resuming at 8-8 heading into the final session, the pair shared the first four frames to make the score 10-10 at the mid-session interval.

Frame 18 proved a particularly dramatic one as after Selby made a break of 53, Saengkham stole it was a 54 clearance.

After the mid-session interval, Selby went ahead again at 11-10 before coming from behind to take frame 22 with a 92 clearance.

Saengkham fought back again to force a decider but after a couple of early chances in frame 25 lost position.

Selby made him pay taking the frame with a break of 124 to seal victory after a match that lasted more than eight hours in total.

A thrilling day's play continued with top seed and defending champion Judd Trump being forced to battle hard before securing a 13-11 win over China's Yan Bingtao in the evening session.

Resuming at 9-7 going into the final session, Trump kept his nose in front but Bingtao was making him work hard to keep his advantage.

Trump clinched a dramatic 22nd frame which lasted more than 50 minutes on the pink to go one away from victory.

Typical of his fighting qualities in the match, Bingtao responded with a break of 130 to close the gap to one frame at 12-11.

Trump completed victory in clinical fashion with a 123 clearance helping him get to the winning line and secure a quarter-final spot.

In the day's other matches, England's Ronnie O'Sullivan, the sixth seed, and China's Ding Junhui, seeded 11, shared the opening session of their match at 4-4, while England's Jamie Clarke leads Scotland's Anthony McGill 6-2, in a battle between two qualifiers.

The second session of those matches takes place tomorrow, as do the first two sessions of two more matches - an all England affair between Martin Gould and Kyren Wilson, who received a bye through to round two after his first-round opponent Anthony Hamilton withdrew, and Australia's Neil Robertson, the second seed against England's Barry Hawkins.