The Rocket was in sensational form in the early stages of the match with breaks of 120 and 121 helping him race to a 3-0 lead.
At that stage, he was considered 1/250 with some bookmakers in-running and looked even closer to victory when 4-1 up.
However, he would fail to win another a frame as mistakes started to creep into his game while a more aggressive Liang starting potting more balls, while benefiting from some lucky breaks, to storm to victory.
The £625,000 prize pool makes the International Championship the most lucrative event in Asia but O'Sullivan will receive just £7,000 for crashing out in the second round.
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Elsewhere, home hero Ding Junhui had an easier time of things than in the first round as he beat James Wattana 6-3 to keep up his bid for a third successive ranking event title.
Two-time world champion Mark Williams crashed out though as he was defeated 6-2 by Norway Kurt Maflin.
World number one Neil Robertson had no such problems though as he enjoyed a 6-1 win over Thepchaiya Un-Nooh while Mark Selby ground out a 6-4 win over Peter Lines.
Results
Peter Ebdon 6-5 Mark Joyce
Mark Selby 6-4 Peter Lines
Liang Wenbo 6-4 Ronnie O'Sulivan
Stuart Bingham 6-4 Martin Gould
Fergal O'Brien 6-4 Rod Lawler
Zhao Xintong 6-1 Barry Hawkins
Neil Robertson 6-1 Thepchaiya Un-Nooh
Ryan Day 6-4 Alan McManus
Marco Fu 6-4 Xiao Guodong
Ding Junhui 6-3 James Wattana
Graeme Dott 6-1 Kyren Wilson
Kurt Maflin 6-2 Mark Williams
Mark Davies 6-3 Stuart Carrington
Mark Allen 6-4 Dave Harold
Joe Perry 6-3 David Gilbert
Matthew Stevens 6-2 John Higgins
- Sports & Recreation
- James Wattana
- Ding Junhui