LONDON, April 27 (Xinhua) -- Defending champion Mark Williams was shocked 13-9 by David Gilbert at the second round of the world snooker championship in Sheffield on Saturday.

The three-time winner's exit means that the top three ranked players in the world have all been eliminated in the first two rounds. World No. 1 Ronnie O'Sullivan was stunned by amateur James Cahill in the opening round and world No. 2 Mark Selby was defeated by Gary Wilson.

Williams had been under treatment in the emergency department of the Northern General Hospital until late last night suffering from chest pains and that obviously has affected his performance.

Former tractor driver Gilbert, competing as a seed at the Crucible for the first time, will next face either Barry Hawkins or Kyren Wilson in the quarterfinals.

Williams said of his illness: "The doctors said they were 99 percent sure it wasn't a heart problem. I'm going to have some more tests when I go home now and see my own doctor.

"I just feel terrible, and I played how I feel, dreadful. I tried my best, but I just had nothing there for the whole match.

"I have loved being introduced as defending champion, it's just a shame I've got to go out this way. I tried my best, I could have easily given up and lost 13-3 or 13-4 but I stuck in there."

World No. 7 Judd Trump took a 5-3 advantage against Chinese top player Ding Junhui.

Trump pulled ahead 5-1 with breaks of 61, 57 and 50. Ding, ranked 10th in the world, halted Trump's run of four frames on the bounce by taking the fifth frame, before a break of 67 saw him end the session just two behind at 5-3. The two players will resume their competition on Sunday afternoon.