Ronnie O'Sullivan claims John Higgins has underachieved in his career but believes the Scot will be full of confidence heading into the Grand Prix in Glasgow.

Higgins matched O'Sullivan's tally by winning his third world title at the Crucible in May, and will be guaranteed strong local support as he attempts to retain his Grand Prix title at the Kelvin Hall.

First up for Higgins will be qualifier Mark Joyce as play gets under way at the nine-day tournament on Saturday.

O'Sullivan believes Higgins is the sport's greatest tactician and is baffled as to why the 34-year-old has not won more world titles.

With World Championship triumphs in Sheffield in 1998, 2007 and 2009, Higgins has established himself as a player to be feared, even if O'Sullivan suggests his trophy cabinet should be better stocked.

World number one O'Sullivan said: "John is one of the all-time greats and I think he's actually underachieved in his career.

"It sounds a strange thing to say, but it's because of how highly I rate him, and I know some of the other players would agree with that.

"He's the best tactical player ever - ahead of Steve Davis - plus he's a heavy break-builder, so he's got no weaknesses.

"Although he's won three world titles, his game is so well suited to the longer-frame tournaments that I would have expected him to win more.

"He's come into this season automatically feeling full of confidence because he's world champion. That's how I was last year and it's a beautiful feeling."

O'Sullivan has 22 ranking event titles to his name, against Higgins' total of 20, and begins his own Grand Prix title bid against Glasgow's Jamie Burnett next Tuesday.