Ronnie O’Sullivan escaped with a slap on the wrist after snubbing a mandatory post-match press conference following his first-round with at the Betfred World Championship.

World Snooker announced O’Sullivan was warned and told he will be fined for any further breaches of discipline.

In a statement, World Snooker said: “Ronnie O’Sullivan has received a formal warning from World Snooker following his failure to fulfil media obligations at the Betfred World Championship on Monday.

“This is in line with World Snooker procedure as it is his first breach of contract this season. Any further breaches will result in a fine and possible referral to the WPBSA (World Professional Billiards and Snooker Association).”

Five-time world champion O'Sullivan beat David Gilbert 10-7 to secure his place in the last 16 at the Crucible.

As well as refusing to attend the press conference, O’Sullivan declined to talk to tournament broadcasters the BBC.

In Tuesday’s action, world number one Mark Selby held off a spirited fightback from Robert Milkins to secure his passage through to the second round.

The Crucible had already witnessed four former world champions exit in the first round, with Graeme Dott, Stuart Bingham, Peter Ebdon and Shaun Murphy all leaving Sheffield early, and Selby was in danger of becoming another victim.

Despite the 32-year-old coming into the morning session 7-2 up, Milkins dominated the first four frames to leave the match wide open.

The Milkman took the first three with breaks of 50, 61 and 62 and won the fourth, despite a 60 from Selby, to head into the mid-session interval just one frame adrift of the 2014 world champion.

Selby, though, regained his touch by winning the next three frames – the last after a re-rack – as breaks of 67 and 70 helped to seal a 10-6 victory. He will face qualifier Sam Baird in the next round.

Selby told BBC Two: “I went out there knowing that Robert was going to come back at me, and he played some great stuff to get himself back to 7-6 and back into the match.

“The interval came at a great time for me and the wrong time for Robert. I managed to regroup, go on the practice table and hit a few balls and get a bit of rhythm and that stood me in good stead.”

On those potential challengers for the title who have already fallen in the first round, Selby added: “I suppose on paper you would say it is a shock, but when you look at the players they have been beaten by it isn’t really.”

Selby has missed the past two tournaments – including last month’s China Open, a tournament he won in 2015 – and he says the rest could prove to be worthwhile.

He said: “I felt fresher, but then at the same time I wasn’t as match sharp. There were positives and negatives really.

“For a couple of years I’ve been to China and managed to do well and get to the latter stages and then flown back with jet lag and not really gone on a good run (in Sheffield).

“The last thing I want to do is come here and not put in a good performance and, if I was to lose in the first round, at least I can hold my hand up and say I gave it my best shot.”

Australian Neil Robertson, another former winner at the Crucible, has work to do if he is to avoid an upset after Nottingham’s Michael Holt impressed during the opening session of their first-round clash to lead 6-3.

Holt flew out of the traps to take the first two frames and a superb break of 140 – the highest in this year’s tournament so far – in the third left the 2010 world champion reeling.

Robertson, though, fought back to claim the fourth frame to give himself a foothold and he responded in fine style after the mid-session interval.

The world number four rattled off successive centuries of 101 and 107 to draw level at 3-3, but Holt was not to be outdone and hit back with breaks of 115 and 50 to help regain a three-frame lead heading into Tuesday’s decisive evening session.