Wales moved top of World Cup Pool A after claiming a third successive win that left host nation England one defeat away from elimination.
Although Wales triumphed 23-13 at the Millennium Stadium, they were made to sweat profusely by a Fiji side that enjoyed scrummaging supremacy and consistently threatened a major World Cup upset.
In the end, tries by outstanding scrum-half Gareth Davies and hooker Scott Baldwin - plus 13 points from fly-half Dan Biggar's ultra-reliable right boot - edged Wales home.
Fiji replied through a brilliant Vereniki Goneva try, while fly-half Ben Volavola booted a conversion and two penalties, yet Wales had just enough in the tank to get home.
It means that England must beat Australia at Twickenham on Saturday - a bonus point draw would also keep them afloat - or they will face the humiliation of exiting their own World Cup after just 15 days.
Wales, though, have by no means secured a safe quarter-final passage themselves, and their fate could boil down to a Twickenham showdown with Australia on Saturday week if England beat the Wallabies and then claim an expected five-point maximum against Uruguay.
That situation would have been alleviated to a degree had Wales collected a bonus point, but the ferocity of Fiji's performance meant there were times when not even victory could have been taken for granted.
Wales ultimately dug deep just five days after their Twickenham heroics saw off England 28-25, and even though Biggar gingerly left the action seven minutes from time, there were no apparent fresh injury setbacks.
Head coach Warren Gatland has lost almost a sixth of his original 31-man World Cup squad to injuries, and he will be grateful that Wales do not play again for another nine days.
Gatland's men can now sit back and relax on Saturday and watch one of England's biggest games since they won the World Cup 12 years ago, knowing that an England loss would mean they march on and secure a last-eight place.
The opening five minutes were played at a madcap pace, with Wales immediately making their intentions clear through a superb George North break before the forwards battered away at Fiji's line.
Although Fiji initially held out, it could not last, and Wales went ahead through a seventh-minute touchdown from Twickenham try hero Davies when he threw a dummy pass to Fiji's last line of defence before crossing unopposed.
Biggar added the conversion, but Wales' Twickenham nemesis - their scrum - soon resurfaced as Fiji established early set-piece supremacy before opening their account through a Volavola penalty.
Wales briefly lost a bloodied Bradley Davies and wing Alex Cuthbert from the action - they returned following temporary appearances by Luke Charteris and Lloyd Williams - but even though a Biggar penalty made it 10-3, it should have been a more convincing lead, given full-back Matthew Morgan's attacking brilliance.
But Wales did not deviate from their attacking philosophy, and a superb Biggar break ultimately freed World Cup debutant Tyler Morgan in space. And when Morgan was tackled short, Baldwin picked up to crash over.
Another Biggar conversion made it 17-3, yet Wales could not escape their scrummaging problems, and a second successful Volavola penalty as a direct result of those issues cut the deficit to 11 points at half-time.
Wales needed to assert authority early in the second period, but the complete opposite happened as Fiji grew in confidence on the back of a dominant scrum.
And they breached Wales' defence in spectacular fashion, cutting loose from deep when wing Asaeli Tikoirotuma sprinted clear, and a stunning move ended with Goneva touching down, before Volavola's conversion underlined it was emphatically a case of game on.
Wales desperately had to calm things down, and that influence predictably arrived through Biggar, who landed a long-range penalty for his 12th successful World Cup kick from 12 attempts.
There was no pattern or predictability to the game, which unquestionably suited Fiji more than their opponents, yet another Biggar penalty opened up a 10-point advantage and Fiji finally had no reply.