World champion and home favorite Mark Williams was knocked out of the Welsh Open in a surprise defeat after losing 4-2 to China's Zhang Anda in the second round in Cardiff.

World No.2 Williams praised Zhang, ranked 81st in the world, “he played much better than I did. I don't know why his ranking is such low.”

This is the second time a Chinese player has beaten the three-time world champion. Last week, he lost to China's 18-year-old Yuan Sijun in the first round at World Grand Prix.

However, Yuan didn't make miracles again on Wednesday, as Ronnie O'Sullivan came from behind to beat him 4-2. 

“Yuan is an incredible player. He has the potential to win a world title and will become a superstar in China if he keeps up his form,” said O'Sullivan.

At the same time, Ding Junhui beat Oliver Lines 4-3 and will face Joe Perry in the next round. Ding has a 14-6 win-loss record during their previous encounters.

Ding beat Mark Selby in the 2012 Welsh Open to win the championship, and he took the runner-up in 2014.

China's Zhao Xintong has also made it through to the next round, while other Chinese players have been out in the Welsh Open.