Northampton staged an heroic fightback at Croke Park before being ejected from the Champions Cup in agonising fashion as a James Lowe hat-trick propelled Leinster into yet another final.

The Premiership leaders came to Dublin as clear outsiders against the perennial challengers for the ultimate prize in European rugby and when they trailed 20-3 shortly after half-time, it threatened to turn ugly for the Saints. They had played ‘Murder on the Dancefloor’ in the stadium before the delayed kick-off and oval-ball murder appeared to be on the cards, but it didn’t turn out that way.

Normally, when Leinster go for the jugular, they don’t miss. But in what was a one-sided semi-final for so long, the hosts couldn’t put their English rivals away. Instead, the visitors climbed out of a deep hole and tries by George Hendy and Tom Seabrook brought them to the brink of an epic upset before the Irish province clung on to clinch their place in the showpiece at Tottenham Stadium on May 25.

There, they will face either Toulouse or Harlequins and strive to secure a record-equalling fifth title. Meanwhile, Northampton will hope to shake off the disappointment of this near-miss and focus on trying to win the league, from their current position of strength.

At the final whistle, Saints players held their heads in dejection. They had come so close to a result which would have gone down as one of the club’s greatest, from a position of extreme adversity. But defeat meant an end to the European career of the magnificent Courtney Lawes, who led his team with typical authority, ahead of a summer move across the Channel to Brive. He will miss these huge fixtures, against the great and the good — and they will miss him.

A hat-trick of tries from James Lowe booked Leinster's place in the Champions Cup final

Northampton started the game in jittery fashion. In the ninth minute, hesitation in the visitors’ defence meant Leinster were handed an attacking scrum and they built the platform for their first try. Another penalty followed in front of the posts, Jamison Gibson-Park took it quickly and his long pass over the stranded Alex Mitchell picked out Lowe, who burst past Hendy to score. Ross Byrne added the conversion.

Northampton were stuttering and reeling, and it went from bad to worse for Dowson’s side as Fin Smith’s pass near halfway was intercepted by rival No 10 Byrne. The fly-half was chased down, but Leinster again made their territorial advantage count. This time, from a drive in the 22 and a solo surge by Caelan Doris, Gibson-Park batted the ball left where Lowe was free to touch down again.

Byrne couldn’t land the extras from a tight angle, but it was 12-0 and a procession seemed on the cards. The Saints needed a spark of defiance. Lawes duly obliged, winning a trademark turnover in front of his own line. At long last, the visitors built some pressure. They couldn’t break the shackles fully, but a Smith penalty sent them into half-time merely 15-3 down. It could have been a damn sight worse.

Sadly for Northampton, it soon was. In the 44th minute, Ryan Baird’s barnstorming break into the opposition 22 set the wheels in motion for another Leinster strike. They were repelled on the right, but good hands by Jamie Osborne and Dan Sheehan kept the raid in motion and Ciaran Frawley sent Lowe over to complete his hat-trick in the left corner. That was it; game over. No way back.

Or so it seemed. From nowhere, the Saints ignited. Juarno Augustus rampaged down the right and after Leinster made a mess of a lineout, the ball was switched left where Hendy kicked ahead and pounced on a spill by Jordan Larmour to score. Smith kicked the conversion, then Byrne missed a straight penalty shot at the other end.

There was a hint of tension around as an actual contest broke out, belatedly.

Northampton came again. Tommy Freeman kicked ahead on the left, ran like the wind in pursuit and forced Gibson-Park to concede a five-metre scrum. The visitors turned the screw, kept forcing penalties and eventually Seabrook was released to score on the left. Smith converted and it was a three-point game.

With a minute remaining, the Saints swarmed forward seeking a match-winning try. The force seemed to be with them, but Jack Conan won a turn-over, Croke Park erupted and a shock was averted.