 Complete the following phrase:  In 2007, OSullivan won his third Masters title and his fourth UK Championship, his first ranking title in almost three years. He won his third world title in 2008, defeating Ali Carter 188 in the final, after which he held the world number one ranking for the next two seasons. He added his fourth Masters title in 2009. After two seasons that saw him fall out of the top ten in the world rankings for the first time, he began working with psychiatrist Steve Peters in 2011. A resurgent OSullivan captured his fourth World Championship in 