Leinster Rugby kicked off their Heineken Champions Cup campaign with a five-try win at Montpellier’s GGL Stadium.

The province had to cope with the late loss of Johnny Sexton from the replacements, meaning the promotion of Harry Byrne to back-up his brother on the bench.

Full-back Jimmy O’Brien, making his European Cup debut, and centre Ciaran Frawley, starting at this level for the first time, needed to get into the game smartly.

Both men benefited from an early hit by Hugo Keenan on Paul Willemse to get their hands on the ball in Leinster’s first attack. A thumping tackle by Arthur Vincent and a surging counter ruck enabled the home side to clear downfield.

Luke McGrath was called on twice to launch balls from the base and control a Montpellier punt in a busy opening for the scrum-half.

Rhys Ruddock and Devin Toner, in a double tackle, and Caelan Doris made physical statements. Michael Bent was the arrow in a superb first scrum, drawing a penalty, before McGrath made significant ground into the 22.

They stayed patient. Robbie Henshaw, Ross Byrne and O’Brien then flashed picture-perfect passes to send Josh van der Flier into the right corner for the opening try in the sixth minute.

From the restart, Leinster were well-organised. The chase and challenge from Keenan caused a spill, seized on by Toner, so that the visitors could move again.

The loss of Leinster’s first lineout was remedied by van der Flier’s seizure of the ball from Jacques du Plessis on the floor, accruing a penalty for Byrne to nail for 8-0 in the 10th minute.

Once again, they carried from the kick-off, Doris knifing between two defenders and O’Brien earning a penalty for a high hit by second-row Bastian Chalureau.

The combination of Alex Lozowski and Vincent opened the gate for a try-scoring chance, the return pass slipping away from Lozowski. The agile O’Brien cleaned up the mess and Leinster edged the ensuing kicking contest when McGrath was quick to the ball and the French lost their discipline at the ruck.

The Blues were full of running in the wide channels.

On the other side of the ball, they looked comfortable until Scott Fardy was caught on the wrong side of a ruck with James Tracy in position for the steal, scrum-half Benoit Paillaugue kicking three points.

The contest of Keenan from the restart was exemplary, allowing prop Peter Dooley to show his handling skills before Henshaw probed the corner with a pinpoint punt.

The poise of Dave Kearney in taking the ball back was backed up by the continuity of backs and forwards with Toner and Tracy to the fore.

Scrum-half McGrath kept peppering the short side, Henshaw’s stunning offload and another from Ruddock concluded with Frawley’s left-handed finish in the corner for 13-3 in the 27th minute.

There was a degree of sympathy for Henshaw when he was whistled for a penalty in ripping the ball away in the tackle, Paillaugue striking for the second time.

The response was superior, Leinster looking to shift the ball at every opportunity.

The upper body strength of No 8 Doris forced a turnover, van der Flier gobbled up the metres and Byrne calmly kicked crossfield for Kearney to collect a cracking try on the left, Byrne converting.

However, McGrath twice had to come to the rescue deep inside the 22, as Vincent and Paillaugue kicked dangerously, and Fardy stole a lineout to close out the half.

Montpellier were in a hole and the temptation to try something magical almost cost them dearly. Fardy rushed up on Gabriel N’Gandebe without getting the break of the ball.

The French looked far more enthusiastic than in the first period and Paillaugue kicked another three when Doris was penalised to make it 20-9 in the 43rd minute.

Leinster went back to their ball movement and weaved patterns left and right with a beauty of a ball from Dooley to Henshaw almost sent Kearney away with an offload.

A new-look Leinster scrum provided momentum with O’Brien’s left-footer moving the needle, in terms of territory, and a subsequent ‘tumbler’ forced Montpellier to defend from a five-metre lineout.

They escaped the pressure through a Bismarck du Plessis poach, a scrum penalty and a knock-on in the air.

It took an unbelievable fetch from Henshaw to put Leinster back on the front foot. They came hard onto the ball from Toner’s lineout take, van der Flier hitting the line at speed to claim a penalty.

They opted to tap and go from close range only to take the points when another penalty immediately came their way, Harry Byrne making it 23-9 not long after coming on for his European bow.

The visitors got out of jail when Montpellier were pinged for playing Andrew Porter without the ball to create a hole for Paillaugue.

Back-to-back penalties were punished by Harry Byrne’s line kicking and the Leinster maul powered up for Dan Leavy to snatch the bonus-point in the 70th minute.

Then Leavy kept Bismarck du Plessis from grounding the ball on the line.

N’Gandebe was able to took his chance in the 77th minute – Montpellier’s first try.

There was still enough time for O’Brien to counter from deep and get back into position to take Henshaw’s tap down from a speculative kick for a fine try in a superb individual performance, Byrne converting for a convincing victory.