The Welshman produced the type of scoring form that saw him lift the world title for a third time in May with some terrific play, compiling knocks of 78, 63, 52 and 75 on his way to the last eight.
He will face Jack Lisowski on Friday for a semi-final spot after the Cheltenham player hit back from 3-0 behind to complete a 5-4 victory over Kyren Wilson in a thrilling match that could have gone either way.
Williams pulls off World Open comeback to win title
Despite making breaks of 66 and 56, world number 24 Lisowski somehow lost the first three frames, but rallied strongly with runs of 73, 56, 59 and 75 helping him force a decider.
The match could have gone either way, but Lisowski won it on the final pink to earn a merited win over the World Championship semi-finalist.
World number one Mark Selby is out of the tournament after losing 5-4 to world number 53 Noppon Saengkham in a match that ran for four hours and 26 minutes.
Selby clawed his way back from 3-0 and 4-2 behind to force a decider boosted by a 102 run in the fourth frame, but lost the match on the black to suffer a shock defeat.
Marco Fu produced some imperious form as he overwhelmed Robert Milkins with knocks of 78, 118, 58, 103, 93 and 96 in a 5-2 win.
WORLD OPEN LAST 16 RESULTS
- Mark Selby 4-5 Noppon Saengkham
- Xiao Gudong 5-3 Anthony Hamilton
- Kyren Wilson 4-5 Jack Lisowski
- Joe Perry 1-5 Mark Williams
- Robert Milkins 2-5 Marco Fu
- David Gilbert 5-3 Ricky Walden
- Barry Hawkins 5-4 Matthew Selt
- Fergal O'Brien 2-5 Gary Wilson
- Marco Fu v David Gilbert
- Barry Hawkins v Gary Wilson
- Noppon Saengkham v Xiao Gudong
- Jack Lisowski v Mark Williams
Willams produces stunning comeback to reach semi-finals