Lines turned professional in 1991, and in his debut season managed to reach the last 32 stage twice, at the 1992 Strachan Open and the 1992 Asian Open. Wins were hard to come by for him during the next few seasons, although he managed to qualify for the 1995 International Open, beating the likes of Fergal O'Brien and Doug Mountjoy in the process. Lines briefly fell off tour in 1997 but returned immediately via Qualifying School, and his results started to improve. 1997/98 season saw him reach the last 32 of the Welsh Open and Scottish Open before coming through qualifying for the World Championship to reach The Crucible for the first (and to date only) time in his career; there he was beaten 10–4 by John Parrott but not before compiling a 141 total clearance - the highest break by a debutant. As a result, he finished the season ranked 53, and rose to 42 after the next season despite having failed to reach another last 32.