Former world number one Mark Allen fought back from an "absolutely embarrassing" first session to beat China's Zhang Anda 10-6 and move into the last 16 of the World Snooker Championship.

Northern Ireland's Allen trailed 5-3 after Saturday's first session at the Crucible, without making a single break of 50, and spent the evening "having some drinks with my mates, a few more drinks, some bets and watching the football".

But on Sunday, he looked a different player.

The 40-year-old produced a magnificent clearance of 140 in frame 11 to start his recovery, following that with a break of 109 in frame 12.

His third century in five frames came in frame 15 with an effort of 129 to move one away from victory, which he sealed with a break of 81 in the 16th frame.

Zhang, who has lost in the first round on all of his six Crucible appearances, scored only 42 points in the last six frames as Allen stormed into the last 16.

"I was so frustrated yesterday – I've been doing things so well on the practice table, being in the gym and eating well," said Allen.

"After that match yesterday I just went out and had a few drinks and a burger.

"I thought, 'I can't play any worse than yesterday'. I was so down on myself, I didn't want to talk to anyone after that session yesterday.

"So I went out, had a few bets and watched the football with my mates. A bit of bad food… and slept really well last night and played much better today."

Allen, who will play either 2024 champion Kyren Wilson or 19-year-old Stan Moody in the next round, admitted he did not see the match panning out how it did.

"Yesterday was absolutely embarrassing, very frustrating and I was completely gutted with my performance," said Allen. "I came in today with less expectations but when you're out there you realise how much you want it and the fire in your belly comes back.

"I can't have many more sessions like I did yesterday. I got away with one there. It's not good enough at this level. That second session was decent but I've been here for 20 years and I would like to think there's been better ones.

"I need to be doing that every single time I play here. Ronnie [O'Sullivan], [John] Higgins and [Mark] Selby produce that type of session every time."

Allen has reached the semi-finals of the World Championship twice, in 2009 and 2023, and has won two-thirds of snooker's Triple Crown – the Masters in 2018 and the UK Championship in 2022.

He has won a total of 12 ranking titles and had a three-month spell as world number one in 2024 but he admitted his career would feel incomplete if he did not secure a World Championship title.

"I'm not going out drinking on Wednesday. I just felt something needed to change (…) If I hadn't done that I would've imploded," said Allen.

"I want to be world champion. It will be a disappointing career for me if I look back and I haven't won it.

"I just want it so much – I would rather have that feeling than not care. You want to win the World Championship – that's why you start to play as a 12-year-old."

China's Ding Junhui holds a 7-2 lead over England's David Gilbert after a dominant opening session.

Gilbert, 44, a two-time semi-finalist, won two qualifying matches to get to the Crucible but did not score a point in four of the nine frames and collected only 83 points in the final seven frames.

Ding, who lost in the 2016 final, made breaks of 94 and 100 and is only three frames away from sealing a last-16 tie against compatriot Zhao Xintong, the reigning champion.

In the afternoon session, four-time winner John Higgins takes on two-time runner-up Ali Carter, while Barry Hawkins holds a 7-4 lead over Matthew Stevens after their first session.

Three-time winner Mark Williams is leading 6-3 against Polish debutant Antoni Kowalski, 22, and the game resumes in Sunday's evening session, while Xiao Guodong leads 5-4 against fellow Chinese player Zhou Yuelong.