The Scot beat O'Brien 5-3 to set up a showdown with Williams after the Welshman beat England's Jamie Cope 5-3. Higgins did not have things all his own way in Beijing. Having produced 74 and 50 to go 3-1 up, O'Brien clawed one back and made a fight of it until Higgins finally settled matters with a 74 in the eighth frame.
"I'm very happy to win but there were lots of mistakes from the two of us," Higgins said. "If I play like that against Mark I'll lose. The last time I played him here was in the final four years ago and I lost 10-9, so I owe him revenge.
"There's always pressure on your first-round game so hopefully I'll have more confidence in my next match."
Sheffield-based Ding Junhui, the home favourite, survived a scare to beat Gerard Greene 5-3 and move into the last 16.
The 22-year-old will meet Mark Selby or Rod Lawler after eventually making two centuries and overcoming the England-born Northern Irishman.
Ding lost the opening frame before bouncing back to claim the next four and though he allowed Greene back in to make it 4-2, an impressive 107 saw him through.
Mark Allen will face Stephen Maguire in the next round after his 5-1 win against Graeme Dott featuring breaks of 102, 60 and 86.
Ryan Day advanced with a 5-1 win against Robert Milkins and Neil Robertson saw off Mike Dunn 5-2 to book a meeting with either defending champion Peter Ebdon or Judd Trump.
Marco Fu saw off little-known Belgian Bjorn Haneveer 5-2 and will next face Shaun Murphy or Nigel Bond.