O’Sullivan, who captured the World Championship last May and the Northern Ireland Trophy in August, defeated Joe Perry 5-3 on a day when Jamie Cope made a maximum 147 break and still lost his match.
Cope became the 10th player to compile more than one maximum in professional competition but was still beaten 5-2 by Mark Williams.
His maximum came in the third frame of his match against Williams and should earn him £22,000 (€28,000), but after winning the fourth frame the 23-year-old lost three in succession as his hopes of reaching the quarter-finals were sunk.
Welshman Ryan Day defeated two-time world champion John Higgins 5-3 while world number two Stephen Maguire beat Stuart Bingham 5-3.
In earlier action, Welsh Open champion Mark Selby beat Mark King 5-0 to storm into the quarter-finals.
The 25-year-old world number four compiled breaks of 48, 68, 48, 44 and 68 to set up today’s last-eight meeting with Marco Fu, who overcame Andy Hicks 5-2. Selby said: “I played really well.
“I didn’t have many big breaks but I didn’t give anything away either.
“I’ve played well in China over the last three tournaments so hopefully I can go one better this time.”
World number 35 Ricky Walden pulled off a stunning 5-4 victory over Australian Neil Robertson, having been 4-1 down.
Six-time former world champion Steve Davis also advanced after a similar win against Northern Ireland Trophy finalist Dave Harold.
Veteran Davis came from 3-0 and 4-1 behind to claim a 5-4 win.