Nadolo powers Montpellier to first win
The giant wing rumbled over for a first-half try, before capitalising on an interception - after Vincent Martin had gone over after half-an-hour.
But Leinster grabbed a crucial losing bonus point in the last play of the game, when Isa Nacewa darted over and converted his own try.
The point keeps Leinster top of Pool Four with six points, but only two points separate them and bottom side Northampton Saints after two rounds.
Montpellier had most of the possession and territory in the first quarter but failed to turn pressure into points.
Instead, it was the Irish province who finally broke the deadlock after 26 minutes. Leinster rumbled a rolling maul into Montpellier territory before it was brought down illegally. Surprisingly, Isa Nacewa took the kick instead of Sexton and made no mistake to make it 3-0.
But Montpellier hit back four minutes later. Vincent Martin scooped up a loose ball 30 metres from the try-line and scorched past Jamie Heaslip and Mike Ross to score at the posts. Frans Steyn atoned for an early penalty miss to slot the conversion to put the hosts 7-3 in-front.
And it got even better for Jake White's men just before the break. Full-back Joffrey Michel drew his man to give Nadolo a one-on-one against Rob Kearney, and the Fijian giant ran over the Ireland full-back to score at the corner. Steyn landed the touchline conversion to make it 14-3 at half-time.
Steyn extended their advantage with a penalty, but Nacewa clawed three points back from the tee.
But the star of the show Nadolo bagged his second try of the game and Montpellier's third to put them beyond Leinster's reach. Leo Cullen's men had held firm to stop a driving maul and earn a turnover. But when Heaslip peeled off the back of the scrum and attempted a pass to Zane Kirchner, Nadolo was there to intercept and ran in unopposed.
Nacewa landed a third penalty to make it 22-9, and he was at it again when Jamison Gibson-Park found his skipper racing down the left wing to score. And he showed nerves of steel to land the crucial conversion to seal a losing bonus-point.
The scorers:
For Montpellier
Tries:Martin, Nadolo 2
Cons: Steyn 2
Pen: Steyn
For Leinster
Try:Nacewa
Con: Nacewa
Pens: Nacewa 3
Yellow card: Rob Kearney (Leinster, 56)
Teams:
Montpellier: 15 Joffrey Michel, 14 Marvin O'Connor, 13 Vincent Martin, 12 Alexandre Dumoulin, 11 Nemani Nadolo, 10 Frans Steyn, 9 Nic White, 8 Pierre Spies, 7 Akapusi Qera, 6 Fulgence Ouedraogo, 5 Paul Willemse, 4 Jacques du Plessis, 3 Jannie du Plessis, 2 Shalva Mamukashvili, 1 Yvan Watremez.
Replacements: 16 Romain Ruffenach, 17 Mikheil Nariashvili, 18 Davit Kubriashvili, 19 Nicolaas van Rensburg, 20 Wiaan Liebenberg, 21 Tomas O'Leary, 22 Ben Botica, 23 Jesse Mogg.
Leinster: 15 Rob Kearney, 14 Zane Kirchner, 13 Garry Ringrose, 12 Robbie Henshaw, 11 Isa Nacewa (captain), 10 Johnny Sexton, 9 Luke McGrath, 8 Jamie Heaslip, 7 Josh van der Flier, 6 Sean O'Brien, 5 Mike McCarthy, 4 Devin Toner, 3 Mike Ross, 2 James Tracy, 1 Cian Healy.
Replacements: 16 Sean Cronin, 17 Jack McGrath, 18 Michael Bent, 19 Mick Kearney, 20 Jordi Murphy, 21 Dan Leavy, 22 Jamison Gibson-Park, 23 Joey Carbery.
Referee: Luke Pearce (England)
Assistant referees: Ian Tempest (England), Paul Burton (England)
TMO: Jean-Pierre Pellaprat (France)
Source: @ChampionsCup