Conor O’Brien crossed five minutes from time as Leinster finally killed off a ferocious comeback from Zebre to claim a 40-24 victory in Viadana.

When the Guinness PRO14 champions led 21-0 after 22 minutes they looked on course for the simplest of victories.

But the Italian side fought back with three tries before half-time, adding another in the second half to make it a one-score game heading into the final ten minutes.

That was when O’Brien popped up on the left, collecting the ball from Noel Reid to dot down in the corner before Max Deegan completed his double with the final play.

Leinster had burst out of the blocks with a try from Deegan after just seven minutes. The flanker was the man in control as a rolling maul powered over.

Ross Byrne converted and did the same again when Dave Kearney scored the second. It came from brilliant build-up play as the ball went through the backs to give the full-back a clear run to the line.

Byrne then got in on the act himself, dancing through for try number three after some huge pressure from the Leinster forwards to make it 21-0.

Zebre looked shell-shocked but they responded with some territory for the first time, despite the loss of Jimmy Tuivaiti to the sin-bin.

That pressure eventually told, with Giovanni Licata doing brilliantly to offload to Francois Brummer for the try.

They were in again three minutes later as Jamie Elliott went over from long range, reacting fastest to a loose ball in midfield before putting on the after-burners.

They had another by half-time, Gabriele di Giulio crossing in the corner as he slipped out of the tackle of Kearney to get over.

Zebre’s comeback was founded on a powerful scrum, with one notable shove making a real statement as young loosehead prop Daniele Rimpelli stood out.

Trailing 21-19 at the break, Zebre conceded early in the second half as Scott Fardy crossed on the left after the Leinster forwards had sucked in the Zebre defence.

However the Italians hit back once again, Brummer scoring his second after a wide pass from Carlo Canna, again the home side having gone through the phases to create the space.

Zebre gave it everything in the bid for a win, turning down two shots at goal late on to kick to the corner, but they could not find a way over.

Instead it was Leinster who got back into Zebre territory to set up the O’Brien try before Deegan sealed the win at the death from close range.

The victory extends Leinster’s lead at the top of Conference B as they look to defend the title they won at the Aviva Stadium a year ago.