In showery conditions more suited to the Red Dragons, the Welsh needed only a point to finish runner-up in Pool D, and earned it with a bonus-point fourth try right before the interval.
Their quarterfinal opponent next Saturday in Wellington was to be the winner of Pool C, either Ireland or Australia.
"It's something we've worked very hard for for the last four years and it's a great feeling we've got to the quarters now," said outstanding Wales captain Sam Warburton. "We said we wanted to be ruthless from minute one to 80 and we put in a good performance throughout."
Wales scored nine tries, all of them converted, but two of them included forward passes missed by English referee Wayne Barnes.
The Welsh didn't need the assistance, as Fiji finished with a whimper in a World Cup campaign which began full of promise.
Fiji has haunted Wales since the last World Cup, where it won an epic contest to make the quarterfinals. The Fijians then earned a draw in Cardiff less than a year ago.
But Wales well and truly buried those ghosts in Hamilton, despite the fact it was never put under any real pressure from the Fijians, whose confidence hasn't been the same since a 49-3 loss to defending champion South Africa two weeks ago.
Not in any mind for charity, Wales posted its biggest win over Fiji. Centres Jamie Roberts and Scott Williams shared three tries and the others went to wingers George North and Leigh Halfpenny, Warburton, and replacements Lloyd Burns, Lloyd Williams and Jonathan Davies. Flyhalf Rhys Priestland nailed all six of his goalkicks, and substitute flyhalf Stephen Jones was perfect with his four attempts.
Nicky Little, Fiji's caps and points record-holder, shot wide right with his one penalty attempt in the first half, missing a chance to become the fourth man to score in four World Cups.
While all of Wales' tries entertained, the match was not a spectacle. Knock-ons, running repairs to players and too many penalties made for a stop-start match that struggled for any momentum before a crowd of 28,476.
The best tries were in the first half.
Lee Byrne's quick flick-on gave North a meter-wide overlap in front of the grandstand. North curved back inside and offloaded between two defenders to send in Scott Williams in the 17th minute. Priestland's penalty made it 17-0 in the 32nd and the result was as good as certain.
Barnes missed two forward passes in the buildup to Wales' third try, but North starred in the try which clinched a quarterfinal spot.
With the first half almost up, North ran onto tapped down lineout ball from Warburton, sped behind the Fiji defense and offloaded in a pair of tackles to Warburton, who streaked in.
Roberts' second try after halftime should have been disallowed for another forward pass, but two less converted tries for Wales really wouldn't have mattered in the end.
"We've worked really hard in the offseason so we just said we're too fit, we're too big, we're too powerful and hopefully too smart, and we wanted to be ruthless tonight," coach Warren Gatland said. "I was really proud. Tough conditions and I thought the boys went out there and really gave a really good balanced performance."