The Welsh might be forgiven for riding a huge wave of confidence after beating the hosts at Twickenham but concentrating the mind is an injury glut coach Warren Gatland said was the worst the team had experienced in recent memory.
Added to that is a five-day turnaround and the knowledge Fiji are a much improved outfit compared to the side Wales hammered 66-0 in their final pool match at the 2011 World Cup.
"In the changing-room and on the bus the celebrations were awesome but we know we can't allow things to slip," Warburton said at the Millennium Stadium.
"I know the players won't be in the wrong mind set for the Fiji side. It will be so easy to slip up against a completely different side from four years ago. There will be no complacency."
Although Gatland echoed his captain's view that the team needed to put Twickenham behind them and focus on qualifying from pool A, he admitted he had been taken aback by the reaction to Sunday's last-gasp 28-25 triumph.
"I have looked online and have seen the celebrations in Wales in rugby clubs, pubs and on the streets. It's just phenomenal," he said.
"It shows what rugby means to the nation of Wales. We got a massive lift from seeing those reactions. One of the things we said when we left the hotel was that we wanted to make a nation proud. The boys did that."
Gatland knows that Wales will be roared on by the Millennium Park faithful and his team might need the help after losing another three players to injury.
"I was talking to our physio yesterday and he said it was probably the worst run of injuries he's been involved with as a team," Gatland added.
"I don't dwell on it. I can't change it, so I don't think about the loss of players."
All three injuries were to the backline, however, which means the entire pack will back up from the England match with No 8 Toby Faletau and openside flanker Dan Lydiate winning their 50th caps.
"I think Toby is one of the most well-rounded, gifted players I've played with. There's nothing he can't do," Warburton said of his loose forward colleague.
"Dan is world-renowned for his chop tackle and teams are adapting their style now. Both are hugely influential players in our squad and it's a privilege to play alongside them."
