English club Wasps looked like they had beaten the defending champions when Guy Thompson scored in the corner, but Toulon replied with an injury-time try to Wallabies wing Drew Mitchell for a vital 15-11 win.
Running off a perfectly timed pass from Nonu, Mitchell hit the gas and sped away for the crucial try, and the win that takes Toulon to the top of Pool 5.
Nonu and other imports have been receiving some criticism by Toulon boss Mourad Boudjellal since arriving at the club from their headline-grabbing World Cup efforts.
But Wallabies star Quade Cooper believes things are coming together at the ambitious club.
"We are on the right track – we are winning games and the team is beginning to gel. But it is still early days and all we want to do is work hard and continue to get better," Cooper said after the latest effort.
"We know there is a lot more to come because we have a lot of talented players here. We are staying tight as a team."
The result leaves Toulon a point ahead of Wasps in the pool and the French outfit go to Bath in next week's final round of games.
"It's going to be a very difficult game in Bath. All we want to do is keep on improving and start to find a way to win games away from home," Cooper said.
Former Hurricanes and Blues first-five Jimmy Gopperth kicked two penalties for Wasps.