Michael Holt survived a Ronnie O'Sullivan comeback to win 4-3 in the first round of the World Grand Prix in Llandudno.
Five-time world champion O'Sullivan came from 3-0 down to level the match before fellow Englishman Holt took the deciding frame with a break of 76.
Compatriot Peter Ebdon, 30th in the rankings, shocked world number three Neil Robertson 4-3 at Venue Cymru.
Ebdon now faces China's Ding Junhui, who beat 4-3 Englishman Ben Woollaston.
World number 31 Holt made a brilliant 119 and 88 to establish an early advantage against O'Sullivan, but last year's runner-up compiled an 86 as he drew level.
O'Sullivan missed a red to the centre in the decider as Holt set up a second-round meeting with Liang Wenbo or Graeme Dott.
|More from BBC Wales Sport|
|Gatland: Wales better since World Cup|
|Farah set for world half marathon debut|
|Drugs ban for 12th Welsh rugby player|
Joe Perry beat Barry Hawkins 4-0, and fellow Englishman Martin Gould saw off China's Tian Pengfei by the same margin.
In round two, Perry will play the winner of Wednesday's match between Welshman Jamie Jones and England's Kyren Wilson.
Gould faces Michael White or Shaun Murphy, the 2005 world champion, in the next round.
Ryan Day progressed with a 4-1 win over Matthew Selt, while John Higgins beat fellow Scot Stephen Maguire 4-0.
The winner of the Grand Prix will earn £100,000 in prize money.