Champion Williams beaten by world number 81 Thor

Mark Williams tasted defeat, Ronnie O'Sullivan withdrew and Judd Trump and Mark Allen won in Cheltenham

Defending British Open champion Mark Williams suffered a shock 4-1 defeat by Malaysian world number 81 Rory Thor in the first round of this year's British Open at the Centaur in Cheltenham.

Ronnie O'Sullivan withdrew from the British Open on Monday, just hours before he was scheduled to face Manasawin Phetmalaikul in his first-round match, England's Lewis Ullah coming in as his replacement.

Thor, 36, won the first three frames against three-time world champion Williams, with the help of a break of 85 in the second.

Williams pulled one back, before Thor held his nerve in frame five to get over the line and book his place in the second round.

British Open winner in 1997, 2021 and 2023, Williams lost the inaugural Saudi Arabia Snooker Masters final 10-9 to Judd Trump earlier this month but has failed to recapture the form that took him to that decider in his subsequent two events.

For the Welshman, it was a second consecutive loss in the first round of a tournament, the 49-year-old having also exited the English Open at the first hurdle last week.

Trump and Allen through

World number one Trump, world champion Kyren Wilson, Mark Allen, ranked third, and world number eight Shaun Murphy all won their first-round ties.

Trump showed the fine form which has seen him win the Shanghai Masters and Saudi Arabia Masters this season as he saw off Robert Milkins 4-1 in just 50 minutes.

A break of 104, the 999th century of his career, put him 1-0 ahead and he followed that up with an 81 in the next to lead 2-0.

Milkins replied with a 62 to reduce his deficit, but Trump responded with runs of 74 and 81 to progress, the latter break comprising 11 reds and 10 blacks before he broke down.

Wilson, who beat Jak Jones to win the World Championship in May, bounced back from an early exit at the English Open last week to beat Belgium's Julien Leclercq 4-0.

It was also a routine 4-0 triumph for 2005 world champion Murphy against fellow Englishman Ian Burns.

Allen came through a hard-fought encounter with Gary Wilson, the world number three from Northern Ireland triumphing 4-3 to book a meeting with Aaron Hill in the second round, the Irishman having beaten Ding Junhui 4-3.

Allen, the 2022 runner-up, took the first two frames against the 2021 losing finalist but breaks of 78 and 50 helped Wilson draw level, before Allen won a drawn-out fifth, which lasted almost an hour.

A run of 97 drew the Englishman level but Allen came out on top in the decider to advance to round two.

English duo Barry Hawkins and Ali Carter suffered shock defeats.

Wales' Liam Davies, ranked 105 in the world, sealed a 4-1 win against world number 18 Hawkins, while world number 91 Bulcsu Revesz of Hungary beat 11th ranked Carter 4-3.