Leeds were most people's favourites to be relegated back down the Championship but victory over Worcester would guarantee their Premiership status with a game to spare.
And, in Back's eyes, that achievement would rank higher than even his World Cup triumph with England seven years ago.
"Back in 2003, we were one of the favourites in Australia and we had almost unlimited resources to achieve our goal," said Back, who started in a back row that included fellow Lions Lawrence Dallaglio and Richard Hill in that historic final against the Wallabies.
"However, this season not many people have given us a chance of staying up and yet after our win at London Irish we now know that our fate is in our own hands this Sunday against Worcester."
Having taken over at Headingley Carnegie last season, Back led the side to promotion at the first attempt and has since seen them climb to ninth in the Premiership standings following five wins in their last 10 league games.
And with just two games left to play, Leeds are currently six points clear of bottom-placed Worcester and also ahead of both Newcastle Falcons and Sale Sharks in the race to avoid the drop.
"There is a lot at stake on Sunday but we need to focus on the job in hand and making sure we do the little things right," added Back, who remains the oldest-ever Test Lion following his appearance in the first international against the All Blacks in 2005.
"We have got a very loyal band of supporters and they will be out in force on Sunday. We hear there is an army of fans coming up from Worcester so I hope that the Yorkshire public turn out in force to support the team, the players certainly deserve that after their efforts this season.
"Having watched Worcester we know they are going to be incredibly difficult to beat. They have conceded fewer tries than any other team in the bottom half of the table and despite being bottom they have the leading points scorer in the competition in Willie Walker.
"They will come to Headingley Carnegie fighting for their lives but we have to make sure that we produce our best performance.
"We have been written off but nearly everyone outside of the club but we have never lost our belief and that is key."