Mark Williams said he was lucky to edge out fellow Welshman Ryan Day in snooker World Grand Prix in Llandudno.
Twice world champion Williams earned a last 16 match with Ricky Walden after sinking a deciding black in the final frame against Day.
"I got lucky didn't I," said Williams after fluking a pink before potting the decisive black.
"It was a ridiculous fluke really, but I suppose when you're on a bit of a run you get those things."
Williams' luck did not extend to another former world champion John Higgins, who failed to repeat his recent success at the Welsh Open when he was beaten 4-3 by fellow Scot Graeme Dott.
Judd Trump edged ahead in the race for the highest-break bonus by making a 140 clearance in a 4-0 win over Welsh veteran Dominic Dale.
Dale's compatriot Michael White, winner of the Snooker Shootout and Indian Open already this month, saw his highly profitable recent winning run reach its end as he fell 4-2 to Robert Milkins, who will face Ronnie O'Sullivan for a place in the quarter-finals.
13:00 GMT: Matthew Selt v Stuart Bingham, Neil Robertson v Mark Davis.
14:00 GMT: Ricky Walden v Mark Williams, Joe Perry v Judd Trump.
19:00 GMT: Liang Enbo v Graeme Dott, Robert Milkins v Ronnie O'Sullivan.
20:00 GMT: Mark Selby v Martin Gould, Stephen Maguire v Peter Edbon.