Ronnie O'Sullivan continued his march in Bucharest by beating Northern Irishman Mark Allen in the last 16 of the European Masters.

The five-time world champion, who missed the first four tournaments of the season, secured his third win of the week and booked his quarter-final spot with a 4-2 victory against the Northern Irishman.

Allen raced to the first frame with a break of 121 but poor positioning and then a kick respectively cost him in the next two frames and on both occasions O'Sullivan cleared and won by potting the final black.

O'Sullivan went in off the brown attempting a safety shot in the fourth, allowing Allen to steal in and take the frame on the black.

But the Englishman was finding his groove and breaks of 77 and then 80 secured a last-eight spot, where he will face Mark Davis or Liang Wenbo.

Earlier, Ricky Walden, the world number nine, was stunned by Alfie Burden, who sits 56 places below in the rankings.

Walden battled back from 3-1 down to take the game to a deciding seventh frame but a break of 64 helped the 39-year-old Burden into a ranking quarter-final for the second time in his career.

World number five John Higgins scraped through 4-3 against Tom Ford.

The four-time world champion trailed 3-2 but set up a decider with a break of 71 - his only break of over 50 in the contest - before battling through to a quarter-final meeting with either Judd Trump or Andrew Higginson.

Higgins told "I was very lucky to get through in the end - you always need a bit of luck to win a tournament and maybe that was mine."

In the day's final game, Australia's Neil Robertson produced a break of 103 as he eased to a 4-1 victory against Scottish world number 79 Rhys Clark.