'Surreal' Freeman hat-trick stuns Leinster to take Northampton into Champions Cup final
Freeman crossed inside a 30-minute first-half spell to guide the 2000 winners to their first Champions Cup final in 14 years, claiming revenge for last season's semi-final loss.
The Irish province, four-time champions, miss out on a fourth straight final appearance despite a double from flanker Josh van der Flier.
Northampton will face either Bordeaux-Begles or Toulouse, who meet on Sunday, for the title at Cardiff's Millennium Stadium on May 24.
"We came in as the underdogs, there was no question about that, people said Leinster by 30," Freeman told Irish broadcaster RTE.
"We knew we had this performance in us, if we get our game on the pitch we can take anyone on.
"The hat-trick was a bit surreal, two of them were walk-ins but finding myself in the right position to get on the end of them is kind of my goal."
Leinster's strength in depth, backed by a reported £17 million salary budget, was illustrated by director of rugby Leo Cullen leaving New Zealand centre Jordie Barrett on the bench.
The visitors were without full-back George Furbank due to injury but British and Irish Lions hopefuls such as fly-half Fin Smith, flanker Henry Pollock and in-form Freeman started the game, with the touring side's squad set to be named on Thursday.
Smith boosted his Lions credentials by setting up Freeman's opener to silence the home crowd.
His break from deep and grubber put Freeman in and the playmaker's conversion made the score 7-0 after just eight minutes.
Saints became the first side to score against Leinster since the group stage, after the Irish province claimed two clean sheets in the last 16 and quarter-finals, the first times it had happened in the tournament's 29-year history.
Just before the half-hour mark the hosts underlined their quality as winger Tommy O'Brien and back-rower Van der Flier, another possible Lions inclusion, crossed either side of a Smith penalty to make it 15-10.
Northampton took control of the game just before the break with three tries in eight minutes with Pollock crossing and Freeman claiming his hat-trick for a 27-15 lead at half-time.
The advantage was trimmed to 27-22 after eight minutes of the second half as Leinster captain Caelan Doris, a leading contender to skipper the Lions, smashed over before Barrett was introduced to the fray.
With quarter of an hour to play, Northampton's hopes of a first Champions Cup final since 2011, when they lost to Leinster, was on the horizon as they led 37-27 with full-back James Ramm responding with a try after a Van der Flier touchdown.
Leinster's James Lowe then strolled over and Sam Prendergast slotted the extras to make it a three-point game and set up a tense final nine minutes with the Saints down a man with flanker Josh Kemeny sin-binned.
The hosts pressed on for a winner but lost the ball on the Northampton line with seconds left before Smith kicked the ball to end the game.