 Complete the following phrase:  The 2017 Masters tournament was an invitational non-ranking event held at Alexandra Palace from 15 to 22 January 2017, and saw the 16 highest ranked players in the snooker world rankings compete, with no qualification round. As defending champion, Ronnie OSullivan was awarded number one seed with World Champion Mark Selby seeded second. The remaining places allocated to players were based on the world rankings after the 