Defending champion Judd Trump hit his fifth career maximum break at the Northern Ireland Open on Wednesday.
The world number one made the 147 clearance in the third frame of a 4-0 victory over 16-year-old Gao Yang in the second round of the event, which is being played in Milton Keynes because of the coronavirus pandemic.
It was a brilliant performance from Trump, who hit two other century breaks during the match.
The 31-year-old first achieved the feat in 2013 while his most recent maximum prior to this event came at the German Masters in 2018.
World champion O'Sullivan, meanwhile, came from behind to progress with a 4-1 win over Elliot Slessor.
O'Sullivan had lost his two previous meetings against the world number 56 from Gateshead and was again on the back foot as Slessor opened with a break of 71.
It might have got worse but Slessor missed a crucial red in the second frame and O'Sullivan hit back before easing to victory with breaks of 76, 78 and 97.
O'Sullivan, who will now play Matthew Stevens, told Eurosport: "That's up there with one of the best victories of my career. He beat me twice before. He had the voodoo sign over me and seems to play fantastically well every time he plays me.
"The way he started off I thought, 'here we go again'. I just had to hopefully get a chance.
"Sometimes beating someone like Elliot Slesser in this tournament, in that round, is better than beating someone like (Mark) Selby in the semis of the worlds. Everyone on the circuit knows how good Elliot is. He can play."