 Complete the following phrase:  At the 1973 World Snooker Championship, his first tournament on the professional snooker circuit, Thorburn defeated Dennis Taylor 98 in the first round then lost 1516 to Williams in the second round. Later that year, he had a 40 win over Pat Houlihan at the 1973 Norwich Union Open before losing 24 to Higgins in the quarter-final. In the 1974 World Snooker Championship he defeated Alex McDonald 83 in qualifying then lost 48 to Paddy Morgan in the first round. He started the 197475 snooker season with a victory in the 1974 Canadian Open, knocking out Willie Thorne and Graham Miles to reach the final, where he won 86 against Taylor. He reached the quarter-finals of the 