Two-time victor Williams succumbed 10-8 to Alan McManus while Kyren Wilson battled back from 4-1 down to beat 2006 champion Graeme Dott.
"A lot of people wrote me off against Graeme, even family," said Wilson. "I just wanted to enjoy it because he's such a class player. I'm glad I held my nerve. I can't wait, it's a dream come true.
"I'm going to have a drive past the Crucible now and have a look at it. I've been there to watch my friend Peter Ebdon in the past but it's going to be a bit different playing there.
"I want to draw Ronnie O'Sullivan in the first round proper. He could absolutely batter me but at least I'll enjoy watching him."
Elsewhere, 1997 champion Ken Doherty secured his spot in the main draw with a 10-5 win over Dechawat Poomjaeng and Tom Ford surprised two-time Crucible runner-up Matthew Stevens 10-8.
Qualifying - Round four results
Ken Doherty 10-5 Dechawat Poomjaeng
David Gilbert 10-6 Jimmy Robertson
Kyren Wilson 10-7 Graeme Dott
Dominic Dale 10-6 Andrew Higginson
Alan McManus 10-8 Mark Williams
Michael Holt 10-6 Jamie Jones
Jamie Cope 10-7 Mark King
Tom Ford 10-8 Matthew Stevens
- Sports & Recreation
- Alan McManus
- Kyren Wilson