The five-times world champion lost a scrappy opening frame against his fellow Englishman, but won the next four with breaks of 53, 101 and 47 on his way to completing a comfortable win.
O'Sullivan - who beat Neil Robertson 9-5 in last year's final for a fourth Welsh Open victory - will face Mark Davis in the round of 64.
World champion Mark Selby eased through with a 4-0 win over Liam Highfield.
But home favourite Mark Williams suffered a shock 4-3 defeat to world number 115 Elliot Slessor with Slessor rolling in a closing 90 to complete his progress at the event.
"It's been the biggest win of my career," said 22-year-old Slessor. "I feel like I can win any match, but also lose any match."
Slessor lost the first frame, but won the next three frames boosted by a couple of 50 knocks.
Williams restored parity at 3-3 with runs of 69 and 52, but a fine 90 break was enough to end the Welshman's hopes.
2014 finalist Ding Junhui is also out of the tournament after suffering a 4-2 loss to Robin Hull.
Read the full article on eurosport.co.uk: O'Sullivan eases to opening win in title defence, Williams out in first round
- Sports & Recreation
- Mark Williams
- Mark Selby
- Neil Robertson
- Elliot Slessor
- Mark Davis