The French Top 14 outfit will face reigning champions Saracens in the May 13 final in Edinburgh.
The French Top 14 outfit will face reigning champions Saracens in the May 13 final in Edinburgh after the English side beat Munster 26-10 on Saturday.
Lopez kicked two sumptuous drop goals under pressure to help steady Clermont's nerves after Leinster, the competition's top try-scorers, had stormed back from 15-0 and 21-12 down to move to within a single score.
"That was a tough game. We always knew that they would have a purple patch. We had to start well, hold on when they got on top after half-time and then finish strongly," try-scorer and former Saracens wing David Strettle told Sky Sports.
"I think Saracens have got better since I left, but I can see in the two years that I have been here how important this tournament is to the club."
Despite 17 points from the boot of Johnny Sexton at the Stade Gerland in Lyon, three-time former winners Leinster missed out on a first final appearance since 2012.
"I felt that we could still win it at half-time, we should have made them work harder for their scores. They got a 15-point head-start," said Sexton.
"We were beaten by an impressive side, who have been impressive all year, we have to take our hats off and say they were better than us."
Clermont were off to a flying start as Fiji flanker Peceli Yato easily won a foot race to dive on Strettle's chip ahead to open the scoring on four minutes.
Morgan Parra converted and and added a penalty on nine minutes after Fijian Isa Nacewa was yellow-carded for pulling back Strettle as Clermont were streaking towards a second try.
A man down, Leinster lost their own line-out deep in their territory and Clermont spun the ball wide where Strettle went outside Dan Leavy and cut inside full-back Joey Carbery to score a second try.
Parra missed the conversion though, leaving Clermont 15-0 ahead.
Strettle then made a try-saving tackle as Leinster broke away, taking Carbery around the arms and forcing him into spilling the ball rather than putting Nacewa, returned from the sin bin, away on the overlap.
Leinster finally started to get a hold in the game but still needed Carbery to make a crucial tackle to stop Scott Spedding adding a third Clermont try.
Parra missed a penalty two minutes from half-time and Leinster finally got on the scoreboard just before the break through Sexton's own kick from the tee.
That proved crucial as Leinster were a different proposition after the break and battered away at Clermont, earning three more penalties that Sexton converted.
They even seemed to have gone in front on 56 minutes after a break from Fergus McFadden from inside the Irish half ended with Leavy touching down.
But Welsh referee Nigel Owens pulled the game back to give a penalty to Clermont as McFadden's break was helped by Leavy holding back Aurelien Rougerie.
Parra landed that to give Clermont an 18-12 lead. There was a real feeling that Leinster's chance might have come and gone and Clermont were back in the ascendancy.
Following a period of pressure, fly-half Lopez kicked a sublime drop goal and Leinster were back to two scores behind.
Yet Garry Ringrose produced an individual moment of brilliance, beating two tacklers and selling a dummy to streak through from inside his own half and run 60 metres to score.
Sexton's conversion made it a two-point game with 10 minutes to play.
Leinster were running the ball from deep but crucially gave away a penalty in their own camp as Ringrose held on in the tackle under pressure from Fritz Lee.
Lopez nailed the penalty and four minutes from time added another drop goal as Clermont proved clinical when it mattered most.
A minute from time Sexton pulled back three points with his fifth penalty but Leinster still needed a try and when Clermont claimed the restart, Irish hopes were extinguished.