Sexton to shore up Blues defence
Glasgow v Leinster Live SS Action KO: 1.0
This level of competition is about finding the weakest link and ruthlessly exposing it.
Glasgow coach Dave Rennie is way too canny to have brushed over the five tackles Adam Byrne failed to complete against Montpellier last week.
In fairness, the assignment of controlling the influence of Nemani Nadolo is a thankless one and can leave the best in the business struggling.
It wasn't just the way Byrne was bumped off. It was the hesitency and tentative way he approached his target.
Still just 23, this is far from the end for a real specimen and talent.
He just has to find a way to believe in himself as much as the coaches have done.
For his sins, Byrne has been left out of the squad and the hard-nosed Fergus McFadden recalled to the right wing and Dave Kearney summoned to the bench.
It has been documented how Leinster missed more tackles (34) than any other club last week in the Champions Cup.
Alarmingly, the back division accounted for 26 of them, led by Noel Reid's game-high six.
Scrum-half Luke McGrath (2), out-half Ross Byrne (4), left wing Barry Daly (3) and Joey Carbery (2) were not without blemish.
Even man-of-the-match Robbie Henshaw fluffed his lines four times.
This is where the return of Jonathan Sexton can have the most dramatic change.
"He is such a key leadership figure for us, amazing having his experience coming in," said coach Leo Cullen.
While all the plaudits were lavished on Owen Farrell during The Lions test series in New Zealand, it was Sexton who was the superior force in defence.
For instance, Farrell missed eight tackles in three tests, five in the third alone, against Sexton's one from 24 minutes as a replacement in the first test and from starting the second and third.
So often it is Sexton's vision in attack that is highlighted but his competitive edge in defence which is just as compelling.
In fact, on this occasion the merits of Sexton's defence and, in the absence of Isa Nacewa, how it improves those around him could just be Leinster's best asset.
"When you come up against really good teams like Glasgow, you need to get a lot right," noted Cullen.
"It's making sure we have that level of composure and concentration over the full 80 minutes.
"It is important that we get our defensive set-ups right again so it allows us to attack the game on our terms."
This is where Sexton can give inside centre Reid the confidence to look after his own patch.
Just like wing Byrne, the inaccuracy of Reid in defence against Montpellier is sure to have come to Rennie's attention.
Glasgow playmaker Finn Russell is a magician on the gain line and he will not be shy about asking Reid to make decisions.
While one man, even Sexton, cannot snuff out every danger, or make all the tackles, he will place a demand on those around him to be better than they have been.
Glasgow: S Hogg; T Seymour, S Johnson, P Horne, L Sarto; F Russell, A Price; J Bhatti, G Turner, Z Fagerson, T Swinson, J Gray, R Wilson (capt), C Gibbins, A Ashe. Replacements: P MacArthur, A Allan, D Rae, S Cummings, R Harley; H Pyrgos, N Grigg, L Jones.
Leinster: J Carbery; F McFadden, R Henshaw, N Reid, B Daly; J Sexton (capt), L McGrath; C Healy, S Cronin, T Furlong, D Toner, S Fardy, R Ruddock, J van der Flier, J Conan. Replacements: J Tracy, J McGrath, M Bent, J Ryan, D Leavy; J Gibson-Park, R Byrne, D Kearney.