World champion Ronnie O'Sullivan lost five frames in a row as he was beaten 6-4 by Liang Wenbo at the International Championship in Chengdu on Tuesday.

China's Liang came to Chengdu in form having won the Asian Tour event last week, but few would have expected him to upset the Rocket.

O'Sullivan, in his first ranking event since winning the world title in May, looked like booking his place in the last 16 when he built up a 4-1 lead, but it all went wrong for O'Sullivan from there. 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.

"I was not worrying about the result and went for aggressive shots when I was 4-1 down," said world number 32 Liang, who now faces Mark Davis, a 6-3 winner over Stuart Carrington.

"To lose five frames on the trot is not good - that's a worrying sign," O'Sullivan said.

"This is only my fifth tournament in 18 months, so I am a bit rusty. Only playing in events will rectify that and I've got another four or five tournaments coming up."

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.

China's 16-year-old wild card Zhao Xintong continued his amazing run by beating Barry Hawkins 6-1.

The gifted teenager, having defeated Steve Davis 6-1 and Craig Steadman 6-2, ousted Crucible finalist Hawkins with top breaks of 62 and 63.

World number one Neil Robertson continued his astonishing break-building form with three centuries in a 6-1 win over Thepchaiya Un-Nooh, taking his tally of tons for the season to 38.

Two-time world champion Mark Williams crashed out though as he was defeated 6-2 by Norway Kurt Maflin.