A penalty try plus 11-points from Johnny Sexton gave Leinster a controlling 16-5 lead at the break
Toulon earned their own penalty try, adding to Juan Smith’s first half try to cut the deficit to four points.
Replacement Anthony Etrillard went over to win it for the French side.
Holders Toulon rallied after the break to keep their chances of progression alive as they came from behind to overcome struggling Leinster 20-16 at the Aviva Stadium on Saturday.
The Irish province are enduring their worst losing streak five matches) in their 140 match Champions Cup history and weren’t fancied heading into today’s clash having lost their last three previous meetings with Toulon, which includes clashes against them in the knock-out stages of the last two tournaments.
Nevertheless, Leinster headed into half-time in control with a 16-5 lead following a penalty try and 11-points from the tee via Johnny Sexton but the star-studded visitors kept themselves in the game with an unconverted score from Juan Smith.
But Toulon regrouped and their pack powered past Leinster with a penalty try and Anthony Etrillard’s scores giving the holders the crucial away victory.
Sexton got Leinster on the scoreboard after 10 minutes from the tee before two minutes later Toulon lost Duane Vermeulen as the number 8 was sent to the bin for picking up the ball up from an offside position with Leinster on the attack.
Leinster, with the man advantage, then opened the try scored as Wayne Barnes awarded the hosts a penalty try after Toulon hauled down the Irish provinces drive. Sexton added the simple conversion to edge the host ten points clear.
Toulon though fought back through Juan Smith, who crashed over following some sustained pressure from the French visitors, 10-5.
However, a pair of penalties from Sexton ensured the Irish province headed into half-time in control with an 11-point lead.
Toulon turned up the heat after the break but Leinster’s heroic defence continued to hold strong with Smith, Habana and Mitchell all threatening for the visitor before Vermeulen though he’d got that elusive try but following a trip to the TMO, it was determined the Springbok number 8 was held up after 56 minutes.
Two minutes later though the French visitors got their shove on and Leinster crumbled with referee Barnes having no option but to award the second penalty try of the game. And Taylor converted to bring Toulon right back into this game, 16-12.
The visitors dynamic pack then powered through Leinster’s defence again with replacement prop Etrillard touching down following a powerful rolling maul. The try isn’t converted.
The try isn’t converted but Toulon were able to edge further in front as Taylor slotted an important three points for the visitors from the tee, 16-20.
Leinster’s task was made harder with three minutes left as Jordi Murphy was shown the second yellow of the game.
Toulon looked like sealing it with a minute to play when Mamuka Gorgodze stormed over, though after the TMO was called for it was ruled out for a knock on in the build up. Not that it mattered, as Toulon sealed a scintillating 20-16 victory.
Leinster: 15 Rob Kearney, 14 Dave Kearney, 13 Ben Te’o, 12 Luke Fitzgerald, 11 Isa Nacewa, 10 Johnny Sexton, 9 Eoin Reddan, 8 Jamie Heaslip 7 Josh Van Der Flier, 6 Rhys Ruddock, 5 Mike McCarthy, 4 Devin Toner, 3 Mike Ross, 2 Richardt Strauss, 1 Jack McGrath
Replacements: 16 Sean Cronin, 17 Cian Healy, 18 Martin Moore, 19 Tom Denton, 20 Jordi Murphy, 21 Nick Mc Carthy, 22 Ian Madigan, 23 Zane Kirchner
Toulon: 15 Delon Armitage, 14 Bryan Habana, 13 Mathieu Bastareaud, 12 Ma’a Nonu, 11 Drew Mitchell, 10 Matt Giteau, 9 Eric Escande, 8 Duane Vermeulen 7 Steffon Armitage, 6 Juan Smith, 5 Romain Taofifenua, 4 Jocelino Suta, 3 Matt Stevens, 2 Guilhem Guirado, 1 Florian Fresia
Replacements: 16 Anthony Etrillard, 17 Xavier Chiocci, 18 Levan Chilachava, 19 Mamuka Gorgodze, 20 Juan Fernandez Lobbe, 21 Tom Taylor, 22 Sebastien Tillous-Borde, 23 Konstantine Mikautadze
Date: Saturday, December 19
Venue: Aviva Stadium
Kick-off: 17:15 GMT
Referee: Wayne Barnes (England)
Assistant Referees: Tim Wigglesworth (England), Paul Dix (England)
TMO: Graham Hughes (England)