The 1984/1985 season heralded no progress for Thornley, but in the next, he defeated Derek Mienie of South Africa 10–3 in qualifying for the 1986 World Championship, following this with a 10–7 victory over Patsy Fagan, to reach the last 64. He lost this match 3–10 to Northern Ireland's Tommy Murphy, but earned £1,200 for his effort, and finished the season with a ranking position for the first time, at 97th.