Wales may have been tempted to take sit on their comfortable 31-0 lead at the break, but instead they turned up the heat on Fiji in the second half and in Roberts and wings Scott Williams and George North they have some electric attacking weapons who will cause problems for any defence.
Wales were far too organised and powerful for Fiji and would have gone into this match with the knowledge they lost their last World Cup clash against the Islanders _ a 38-34 defeat in Nantes in 2007.
Big Wales second five Roberts opened the scoring after six minutes, showing good footwork to slip through the defence from 20m out.
Tries to wings Scott Williams and George North followed, Williams showing particularly good footwork to tiptoe down the left touchline.
Roberts scored his second try to open the scoring for Wales after the break, following a brilliant break by wing North and tries to prop Loyd Burns, Leigh Halfpenny, Lloyd Williams and Jonathan Davies followed.
Another positive for Wales was their goalkicking - neither Rhys Priestland nor Stephen Jones missed a shot from 10 attempts.
It was a disappointing way for Fiji to finish the tournament - they would have had high hopes following their quarter-final place four years ago.
They finished this World Cup with just one victory - over easybeats Namibia - and chalked up losses to South Africa and Samoa.
A small victory of sorts would have been a try but Wales denied them even that.
Wales 66 (Jamie Roberts 2, Scott Williams, George North, Sam Warburton, Lloyd Burns, Leigh Halfpenny, Lloyd Williams, Jonathan Davies tries; Rhys Priestland 5 cons, pen; Stephen Jones 4 cons) Fiji 0 HT: 31-0
