Leinster overcame the reigning English champions and league leaders for the second time in six days this evening, but they did it the hard way after enduring a nightmare first half-hour to their Champions Cup tie at the Aviva Stadium.

It’s a win that leaves them in command of Pool 3 with the two January rounds to play and the only question now seems to be whether Leo Cullen’s side can do enough at home to Glasgow Warriors and away to Montpellier to clinch a home berth in the quarter-finals.

None of which looked at all likely around about four o'clock in Ballsbridge as an Exeter side that played much sharper and smarter than the one beaten 18-8 at home last Sunday took the game by the scruff of the neck.

Leinster’s early run of woe took just three minutes to unfold.

By then Sam Skinner had touched down for Exeter’s first try and, as the Chiefs players filed back towards the halfway line, the sight of Jonathan Sexton laying down receiving treatment only added to the pain of such an early blow.

Sexton left for a head injury assessment (HIA) and wouldn’t return. Not ideal at any time or for any player, especially so for Ireland’s playmaker who endured some difficult times with concussion a few seasons ago when employed by Racing 92.

Ross Byrne had four minutes in his pocket as his replacement before he careered into a tackle with Nic White. The Australian scrum-half left to receive stitches and Byrne joined Sexton on the HIA waiting list. So far so disastrous.

Byrne would return but Leinster’s disorganisation was only accentuated by the yellow cards earned by Cian Healy after 18 minutes and Scott Fardy just past the half-hour, the latter as a result of failed attempt to stop a second Exeter try from a maul.

Luke Cowan-Dickie touched down for that five-pointer and, with Gareth Steenson managing a second conversion to go along with a penalty sandwiched in between, the English champions had 17 points on the board.

Leinster just about kept themselves in touch with Isa Nacewa opening their account from a penalty eleven minutes in and clawing back the deficit by six points with another pair in the five minutes before the interval.

They were to prove invaluable foundations for the comeback that followed.

The opening 15 minutes to the second-half were breathless with both sides racking up phase after phase whilst in possession but the two defences were equal to the task and the increasingly inevitable end to every sustained attack was frustration.

Turnovers were ten a penny on either side by then, but Leinster dragged themselves back to within losing bonus-point territory with another Nacewa penalty four minutes shy of the hour-mark before finally earning a sniff of the Exeter try line.

A Jack Conan burst from the back of a scrum on the Exeter ‘22’ brought the province to within five-metres of the chalk, but Fergus McFadden’s lunge over was adjudged to have been held up by referee Pascal Guazere who brought back play for an earlier infringement.

Nacewa’s fifth pot left the home team two behind and then the winning of the game came with a break through midfield by Dan Leavy whose pop pass set scrum-half Luke McGrath under the posts. Yet another Nacewa kick left them 22-17 to the good.

There was another 14 minutes to navigate before the four points could be bagged. Not the faultless, clinical display they offered up in Sandy Park last week, then, but a mightily impressive win in its own imperfect way.

Leinster: R Kearney; F McFadden, G Ringrose, R Henshaw, I Nacewa; J Sexton, L McGrath; C Healy, S Cronin, T Furlong; D Toner, S Fardy; S O’Brien, J van der Flier, J Conan.

Replacements: R Byrne for Sexton (3) and for Larmour (15); J Larmour for Byrne (7); J McGrath for van der Flier (19-28) and Healy (56); J Tracy for Cronin, D Leavy for O’Brien and J Ryan for Toner (all 56); J Gibson-Park for L McGrath and A Porter for Furlong (both 73).

Exeter Chiefs: L Turner; J Nowell, H Slade, I Whitten, O Woodburn; G Steenson, N White; B Moon, L Cowan-Dickie, T Francis; M Lees, S Skinner; D Armand, M Kvesic, S Simmonds.

Replacements: W Chudley for White (7-18 and 63); H Williams for Francis (53); A Hepburn for Moon (56); J Hill for Lees (61); S Hill for Whitten (64); J Yeandle for Cowan-Dickie (66); T Waldrom for Kvesic (69); J Short for Turner (75).

Referee: P Gauzere (Fra).