Last year's beaten finalist, Ken Doherty, trails Joe Swail 5-4 at the end of the first session in their first round match at the World Championships in Sheffield.
The 1997 champion conceded a promising early advantage. The Dubliner led Ulster friend and rival Swail 4-2 and but for a couple of careless misses may have been 6-0 in front.
Swail, who has twice reached the penultimate round at Sheffield, pounced on the errors to turn the tables.
World number six Doherty scored just 15 points in the closing three frames as Swail responded to the challenge with breaks of 127, 41 and 110.
Swail requires five of tomorrow's remaining 10 frames to reach round two.
Defending champion Mark Williams made a solid start against Dominic Dale at Sheffield's Crucible Theatre.
Williams, who became a father for the first time on the eve of the tournament, established a 6-3 lead at the end of the opening session.
lan McManus became the first player through to the second round when his opponent, Chris Small, was forced to retire at the end of the eighth frame.
Small, who suffers from a spinal arthritis called ankylosing spondylitis, experienced an eye problem after being given a steroid injection to treat his back problem.
McManus was leading 7-1 at the time and recorded a 10-1 win when Small forfeited the next three frames.
World No. 9 Matthew Stevens leads Thailand's James Wattana 5-4.