A ruthless Ronnie O'Sullivan extended his winning streak to 18 frames as he cruised into the quarter-finals of the Welsh Open in Cardiff.

O'Sullivan thrashed David Grace 4-0 in the last 32 and returned to action a few hours later to beat Mike Dunn by the same score, racking up 862 points across the two matches and conceding just 57.

The five-time world champion rattled in breaks of 96, 133, 63 and 100 against Grace, who scored just 13 points in reply, while Dunn managed 44 as O'Sullivan made breaks of 84, 69, 117 and 67.

The Chigwell star, who received a walkover in the first round after Robin Hull withdrew, had previously beaten former world champion Graeme 4-0 in round two and also won the last six frames in a row in a 10-3 victory over Ding Junhui in the final of the World Grand Prix on Sunday.

"It was difficult for Mike out there but you've just got to go out and do a job," O'Sullivan told Eurosport. "I'm very confident because I've won a lot of matches so that gives me a slight advantage.

"Winning is a habit and when you get into a winning habit you can even play bad and win in the end. If my form comes good as well it's like a double bonus."

O'Sullivan will expect a far tougher task in the last eight against John Higgins, who also enjoyed 4-0 wins over Sam Craigie and Nigel Bond on Thursday.

Higgins, who beat O'Sullivan 5-0 in their last meeting in the Scottish Open in December, was on course for a maximum in the second frame against Bond, but snookered himself on what would have been the 13th black and had to settle for a total clearance of 144, the highest break of the tournament so far.