The Kangaroos overcame atrocious conditions as they scored six tries and conceded none at Langtree Park to climb to the top of the Group A.
But the result was overshadowed by a sickening injury to Lewis, who dislocated his shoulder after sliding at speed into an advertising sign with 10 minutes to go.
The Cronulla star was assisted off the field in agony and Kangaroos coach Tim Sheens said he would miss the rest of the tournament.
"It took a little while to get back in but they've sorted it. It's definitely the end of his tour.
He's a great tourer, a great member of the squad, the boys love him and he can obviously play so it'll be a big loss for us."
Sheens indicated Australia would look to bring in a replacement for Lewis.
In the Kangaroos' second group game, Daly Cherry-Evans impressed in place of the rested Cooper Cronk at halfback, scoring a try and setting up two others, while five-eighth Johnathan Thurston was named man of the match.
Josh Papalii scored a try on debut while Michael Jennings, Darius Boyd, Josh Morris and Lewis also had four-pointers.
As with their opening win over England, Australia were guilty of some uncharacteristic errors but some sloppy play was inevitable in the conditions.
Australia had the luxury of playing their tournament opener under the Millennium Stadium roof but they were well and truly exposed to the elements in front of around 14,137 fans at Langtree Park.
The match began amid driving rain, strong winds and single-figure temperatures and the conditions acted as a leveller between the sides early on but Australia's class ultimately shone through.
Fiji had never come within 50 points of Australia in three previous meetings but they did an admirable job and captain Petero Civoniceva led the charge as one of the best forwards on the park.
Both teams took time to adjust and it was Fiji who started stronger, opening the scoring with a sixth-minute penalty through Alipate Noilea.
Australia gradually took control of the game and Morris was denied a try by the video referee before Papalii scored in the 16th minute.
The Canberra forward was played into space by a lovely Cherry-Evans ball and barged his way over the line.
Boyd combined with Lewis to extend Australia's lead with a fairly soft try in the 21st minute and Lewis was again involved 10 minutes later as he combined with fullback Greg Inglis to set up Jennings out wide.
Australia were quick to add more points after halftime, with Morris scoring in the corner after Jarryd Hayne did brilliantly to bat back a Cherry-Evans cross-field kick.
Clive Churchill medallist Cherry-Evans scored under the posts in the 57th minute on the back of a James Tamou bust before Lewis finished a well-worked move in the 67th minute.
However the Cronulla star's night ended a short time after as he collided with Jennings while chasing down a grubber and there was immediate concern from his teammates.
New Zealand also had a big win on Saturday night and Shaun Johnson is living the dream as well as living up to his potential.
The 23-year-old halfback has loomed large on the league radar since being touted as the next big thing back in 2009 by Australian legend Andrew Johns.
On Saturday in Avignon, the 2012 international rookie of the year took another step up, scoring half New Zealand's points as they saw off the French 48-0.
"It's just real buzzy, playing a game of footy on the other side of the world," Johnson said.
"It's still kind of surreal."
The Kiwis dominated their second pool B match, running in three first-half tries for an 18-0 lead at the break before adding another five in the second spell.
"I thought the forwards were outstanding, they really laid that platform and I guess us little men could jump off the back of it and that's what we did," he said.
Despite playing on the NRL big stage for the Warriors since 2011, including a starring role in a losing grand final, Johnson says wearing the black jersey at a World Cup tops it all.
"It's just a dream come true to be here."
Although he finished off both his tries in style against France, it was Johnson's kicking and general composure that would have most pleased coach Stephen Kearney.
His tactical kicking was right on the button and his fulltime conversion from the sideline left him with a perfect eight from eight goals.
"I guess that's just my role in the side," Johnson said.
"I'm the goalkicker and my responsibility is to knock them over, so I'm pleased I could do that."
Johnson said the most satisfying aspect of the win was the Kiwis' improvement from last week's patchy opening victory over Samoa 42-24.
His halves combination with Manly star Kieran Foran is also developing nicely, with both players posing threats to the opposition down either flank.
The defending champions have a well-earned couple of days off, before relocating back to Leeds early next week to prepare for Friday's third pool match against Papua New Guinea.