Investec Champions Cup: Leinster v Northampton Saints
Leinster (15) 20
Tries: Lowe 3 Cons: Byrne Pens: Byrne
Northampton (3) 17
Tries: Hendy, Seabrook Cons: Smith 2 Pens: Smith
Leinster advanced to the Investec Champions Cup final with a nervy 20-17 victory over Northampton Saints in Dublin.
Beaten finalists in the past two seasons, Leinster took an early lead through a pair of James Lowe tries and had looked in a commanding position.
The Ireland winger would complete his hat-trick three minutes into the second half but Northampton launched a stirring response, scoring the game's final 14 points as Leinster ended holding on.
The Irish province will now play the winner of Sunday's semi-final between Toulouse and Harlequins at Tottenham Hotspur Stadium on 25 May.
The game was played in front of a Champions Cup record crowd of 82,300 in Dublin's Croke Park, the Gaelic Athletic Association (GAA) ground holding a club rugby fixture for the first time since Leinster beat Munster at this stage of the Heineken Cup back in 2009.
Cian Healy, who came off Leinster's bench to set a new Champions Cup appearance record, was the only member of the home side's squad from that day still present here, but the four-time winners looked right at home early on.
It will be to Northampton's considerable frustration that they played such a hand in allowing the hosts to gain an early foothold.
Both Lowe's tries in the opening quarter of an hour were the product of mistakes from the Saints.
George Hendy's fumble of a Leinster kick gave the opposition the ball before the Saints failed to react to Jamison Gibson-Park's quick tap and the Irish scrum-half placed his pass between two Northampton defenders for Lowe to take on the charge and score.
Northampton were equally complicit in the winger's second, this time the turnover coming from an intercepted pass in midfield.
Ross Byrne did not have the pace to take the ball all the way for the score but when Caelan Doris was stopped short, the ball was popped up and batted out to Lowe to go over again in the same corner.
Against Springbok World Cup winner Jacques Nienaber's rush defence, handling accuracy is paramount but the Saints spilled too much ball to get a foothold in the first half.
Leo Cullen's side were without Test players Hugo Keenan, Garry Ringrose and James Ryan, but Northampton missed their absentees, Ollie Sleightholme and Lewis Ludlum, more keenly, most especially in terms of their carrying.
The Saints, who beat Leinster's Irish rivals Munster at the last-16 stage, could not sustain possession and were punished off their turnovers.
The scrum had been a back and forth tussle but it was off a penalty there on the half hour that Byrne nudged Leinster 15-0 ahead.
Things could have been worse for Northampton but skipper Courtney Lawes' fine turnover five metres out halted a further attack.
When the Saints did finally beat the blitz, working the ball brilliantly beyond the outside cover, the final pass was behind James Ramm and the wing could not gather it in.
Playing with penalty advantage, Fin Smith at least kicked their first three points of the day just before the turn.
Leinster were on the front foot from the restart with the ball worked patiently across for Lowe to score once again in the 43rd minute.
Northampton responded with their most consistent spell of possession but were undone by timely interventions, first from Joe McCarthy and then Andrew Porter.
This fixture has already featured one famous comeback, with Leinster having come from 22-6 behind to win the 2011 final 33-22, and hopes of a similar turnaround were sparked by Northampton forcing a pair of scores late on.
In the 58th minute, when Leinster lost a line-out in their own half, Hendy took advantage of the broken play to kick ahead and gather to give his side a lifeline.
Still 10 points ahead, Leinster looked to respond quickly only for Byrne's penalty to drift wide. Croke Park's partisan crowd cheered as the ball sailed off line, greeting the sight of Ireland head coach Andy Farrell on the big screens.
Northampton would bring the game within a score when Tom Seabrook went over in the 74th minute, doing so after the Saints had fought back to win a scrum penalty.
Smith's conversion cut Leinster's lead to just three and the Saints threatened one of the great comebacks in the final minutes only for replacement back-rower Jack Conan's turnover with 40 seconds remaining to bring one last Croke Park roar.
Still top of the Premiership, Northampton will take plenty from their final quarter back into domestic action.
Leinster, meanwhile, will prepare for their third Champions Cup final in a row.
Leinster: Frawley; Larmour, Henshaw, Osborne, Lowe; R Byrne, Gibson-Park; Porter, Sheehan, Furlong; Molony, McCarthy; Baird, Van der Flier, Doris (capt).
Replacements: Kelleher, Healy, Ala'alatoa, Jenkins, Conan, McGrath, H Byrne, O'Brien.
Northampton: Furbank; Ramm, Freeman, Dingwall, Hendy; Smith, Mitchell; Waller, Langdon, Davison; Moon, Coles; Lawes (capt), Graham, Augustus.
Replacements: Matavesi, Iyogun, Millar-Mills, Mayanavanua, Scott-Young, James, Litchfield, Seabrook.
Referee: Mathieu Raynal (Fra)