 Complete the following phrase:  At the Riga Masters, Robertson did not lose more than one frame in any match as he reached the final. He secured his 12th ranking title with a 52 win over Michael Holt. Robertson reached the semi-finals of the World Open, but lost 62 to Joe Perry. He also played in the semi-finals of the European Masters where he was defeated 60 by Ronnie OSullivan and lost 63 to Peter Lines in the first round of the UK Championship. He was beaten 63 by OSullivan in the quarter-finals of the Masters and was also knocked out at the same stage of the World Grand Prix, 