Leinster’s Jimmy Gopperth had a chance to win the game at the end of normal time but his drop goal attempt drifted wide
TOULON 25 LEINSTER 20
Leigh Halfpenny kicked Toulon into the Champions Cup final at Twickenham next month and kept his team on course for an unprecedented European title hat-trick following an extra-time finish at Stade Velodrome.
The Wales full-back booted six penalties and a conversion of wing Bryan Habana's interception try midway through the additional 20 minutes as Toulon triumphed 25-20 to book a Twickenham final appointment with fellow French heavyweights Clermont Auvergne on May 2.
Leinster gave as good as they got for most of the contest, with centre Ian Madigan kicking five penalties and flanker Sean O'Brien scoring a late try, but it was Madigan's pass that South African speedster Habana intercepted to see Toulon home.
Toulon, bidding to become the first team in 20 years of European knockout club rugby to win three successive tournaments, were pushed all the way by a Leinster side that delivered its best performance of this season's competition.
Ultimately, though, they were left to reflect on what might have been, conceding 13 points during extra-time after holding Toulon 12-12 after 80 minutes.
But Toulon will need to deliver a far more clinical display if they are to threaten Clermont in what will be a repeat of the 2013 European final.
England international Steffon Armitage had to be content with a place on the Toulon bench, providing cover for the back-row trio of Juan Smith, Juan Martin Fernandez Lobbe and Chris Masoe, while Matt Giteau partnered Mathieu Bastareaud in a midfield of contrasting styles.
Leinster, meanwhile, fielded an unchanged team from the side that edged past quarter-final opponents Bath two weeks ago as they looked to reach a fourth European final in the past seven seasons.
Toulon exerted pressure from the start, and they almost went ahead after five minutes when a steepling Frederic Michalak kick failed to be gathered by Leinster wing Fergus McFadden or full-back Rob Kearney, and Toulon skipper Chris Masoe touched down.
Referee Wayne Barnes, though, brought play back for an early infringement after playing advantage, and Halfpenny booted Toulon ahead.
But the lead proved to be short-lived as Madigan passed 100 points in Europe this season with an angled penalty that tied things up, and he landed two further penalties during a four-minute spell that left Toulon with food for thought.
Leinster did not to need to do anything spectacular, it was more a case of keeping pressure on Toulon and making them concede penalties, with Madigan in the mood to gratefully accept his opportunities.
Halfpenny narrowed the deficit via his second successful penalty 11 minutes before half-time, and there remained little to enthuse the crowd in terms of attacking rugby, as both teams seemed intent on trying to dominate midfield exchanges.
Armitage entered the action five minutes before half-time, replacing an injured Smith, but Leinster still held the advantage, having rarely been threatened by a Toulon team that often built solidly, yet lacked a final thrust.
Michalak, who had failed to spark Toulon during the opening half, lasted just eight minutes of the second period before being subsituted, with head coach Bernard Laporte sending on Rudi Wolf and moving Matt Giteau from inside centre to fly-half.
Halfpenny then missed a difficult penalty, but he made amends with a 55th-minute penalty that drew Toulon level and at least breathed life into a game riddled by errors and that cried out for some attacking initiative.
Leinster continued to absorb Toulon's somewhat limited attacking game, and as the clock ticked down, it became a battle of wits and which team could control its nerve.
Madigan showed signs of cracking when a penalty attempt 15 minutes from time hit the post, which gave Toulon an opportunity to counter-attack, forcing their opponents into some frantic defending.
Leinster kept their defensive line intact, but they were punished at the breakdown by Barnes, and Halfpenny's fourth successful penalty made it 12-9.
But Madigan continued to match his fellow marksman blow for blow, finding his range from just inside Toulon's half with a superb strike that levelled things up once more entering the closing 10 minutes.
Gopperth had a chance to win it for Leinster with two minutes of normal time remaining, but his drop-goal attempt drifted agonisingly wide, then Armitage landed a final-kick penalty well short, which meant 20 minutes' extra-time.
Halfpenny and Madigan exchanged further penalties during the early flurries of extra-time, before Toulon's New Zealand World Cup-winning lock Ali Williams was sin-binned for taking out rival lock Devin Toner in the air from a restart.
It appeared a harsh call by Barnes, yet Toulon galvanised themselves via another Halfpenny penalty and Habana's breakaway score that finally broke Leinster, even though O'Brien crashed over from close range with five minutes left.