 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 