Ronnie O'Sullivan blamed a bad cue tip for two sluggish performances despite booking his place in the quarter-finals of the Scottish Open in Milton Keynes.

O'Sullivan won the last two frames to defeat China's Tian Pengfei 4-3 before returning two hours later to see off world number 84 Robbie Williams 4-1.

The world champion was far from his best in either match and told Eurosport: "I was really struggling to get any touch and feel - it was a miracle performance, considering.

"It's like a bullet on there, it's so hard. I am going to have to change it, otherwise I have got no chance."