Leicester ended Toulon's nine-match unbeaten run in Europe as Owen Williams kicked 20 points to see the Tigers home at Welford Road.
Toulon's hopes of exerting a vice-like grip on Pool Three in the European Champions Cup were extinguished after Welsh fly-half Williams booted six penalties and converted lock Brad Thorn's 19th-minute try.
Leicester ultimately prevailed 25-21, but they were made to sweat following an impressive Toulon revival from 13-0 adrift as wings Bryan Habana and Drew Mitchell claimed touchdowns, while fly-half Nicolas Sanchez landed three penalties and a conversion.
While the reigning European champions still top their group, courtesy of a losing bonus point, Leicester have moved themselves firmly into the shake-up prior to next Saturday's quickfire return fixture at Stade Felix Mayol.
The Tigers were hugely-impressive for parts of the game, yet Toulon capitalised on their weaker moments with ruthless efficiency.
But in 22-year-old Williams, Leicester possessed a trump card, as his match-winning haul secured exactly the result that the Tigers needed on a weekend of European action when six English clubs claimed victories - Leicester, Harlequins, Wasps, Northampton, Saracens and Bath.
England front-row forwards Tom Youngs and Dan Cole made their first European appearances of the season after recovering from injury, while red rose lock Geoff Parling was on the bench for potentially his first appearance since mid-September because of concussion.
Toulon, meanwhile, were without injured star backs Leigh Halfpenny and Matt Giteau, but they still paraded a team packed with international talent, including former Leicester prop Martin Castrogiovanni, plus the likes of Habana and Mathieu Bastareaud.
Leicester started strongly, forcing Toulon on the back foot, and a couple of half-chances in attack were followed by a successful Williams penalty after the visitors infringed at a scrum.
And there was no immediate let-up in terms of Leicester's intent, with Williams doubling their advantage through a second penalty awarded when Castrogiovanni charged shoulder-first into a ruck.
Referee Nigel Owens opted not to award a yellow card, but Toulon were rattled, and Leicester punished them with a try inside the opening quarter following full-back Mathew Tait's kick from deep.
Mitchell could not cope with the bounce, struggling to get his hands on the ball, and Leicester's support runners rapidly put him in further trouble as hooker Youngs gathered an off-load and delivered to a supporting 39-year-old Thorn.
Williams' conversion made it 13-0, and despite Sanchez kicking a 22nd-minute penalty, there was no disguising Leicester's dominance. And even when Toulon threatened after a Steffon Armitage break-out, Tigers skipper Ben Youngs covered superbly to snuff out any danger.
Sanchez landed a second penalty, but Williams then turned villain, gifting Toulon an attacking opportunity when his ambitious long-range pass on halfway fell into Habana's hands.
The South African star still had plenty to do, but he gathered possession on the bounce and kept his balance majestically before sprinting clear and claiming a try that Sanchez converted, wiping out the advantage that Leicester had worked so hard to achieve.
It was a case of starting from scratch for the Tigers after the break, having seen their early good work undone, and a third Williams penalty edged them back in front before the game's wholly unpredictable nature witnessed another twist.
On this occasion, Leicester's defence suffered a collective relapse from a scrum just outside their own 22, and scrum-half Sebastien Tillous-Borde capitalised to make an initial break and send Mitchell over unopposed.
Sanchez failed to land the wide-angled conversion, but Toulon were ahead for the first time before they began to utilise their bench by sending on prop Carl Hayman and half-back Eric Escande.
A fourth Williams penalty then edged Leicester back in front during a game of no obvious pattern, then he added another three points that was quickly cancelled out by Sanchez, which heralded a closing 10 minutes with the teams separated by just one point.
But it was the cue for Williams to administer one final blow, bisecting Toulon's posts from the halfway line and leave Pool Three very much in the melting pot.