O'Sullivan lost the first frame he played on the day but then won eight in a row to defeat Chris Wakelin 4-1 in the morning and then Alex Davies 4-0 in the evening.
O'Sullivan fired breaks of 99 and 98 against Wakelin and scored three half-centuries (69, 64 and 53) against Davies before coming from 58-0 down to win the final frame.
He will next face Anthony Gill of Scotland.
Mark Selby also moved on after wins over Rod Lawler and Martin O'Donnell but Judd Trump was defeated 4-2 by Ireland David Morris.
The bottom half of the draw plays to the last 16 on Saturday with Sunday then holding the final four rounds of the tournament.
Round 3 results
Stuart Bingham 4-2 Mark Davis
David Morris 4-2 Judd Trump
Ronnie O'Sullivan 4-0 Alex Davies
Anthony McGill 4-1 Daniel Wells
Robert Milkins 4-3 Marco Fu
Martin Gould 4-2 Jimmy Robertson
Aditya Mehta 4-2 Anthony Hamilton
Mark Selby 4-3 Martin O'Donnell
Round 2 results
Stuart Bingham 4-3 Saqib Nasir
Mark Davis 4-2 Steve Davis
David Morris 4-2 Sean O'Sullivan
Judd Trump 4-2 Graeme Dott
Ronnie O'Sullivan 4-1 Chris Wakelin
Alex Davies 4-1 Stuart Carrington
Anthony McGill 4-2 Peter Lines
Daniel Wells 4-3 Matthew Selt
Robert Milkins 4-0 Dechawat Poomjaeng
Marco Fu 4-1 Joel Walker
Martin Gould 4-0 Ben Jones
Jimmy Robertson 4-1 Tom Ford
Aditya Mehta 4-0 Alan McManus
Anthony Hamilton 4-0 Gary Wilson
Martin O'Donnell 4-1 Michael Leslie
Mark Selby 4-1 Rod Lawler