IRELAND full-back Rob Kearney will win his 121st cap for Leinster on the occasion of his seasonal debut as the final piece in the currently available squad jigsaw in Galway this evening.
Coach Joe Schmidt has continued the culture of change -- there were seven in the first match, 11 in the second and six in the third -- by making 10 for what is always a demanding task.
Worryingly, hooker Tom Sexton will start for the first time in front of locks Tom Denton and Quinn Roux and flanker Ben Marshall as a quartet with no more than eight caps between them, five of those off the bench.
The onus falls heavily onto the shoulders of captain Shane Jennings, loose-head Springbok Heinke van de Merwe and former Connacht tight-head Jamie Hagan to guide them through a raucous atmosphere.
Number eight Leo Auva'a is also back to provide bulk off the base. But the New Zealander looked a yard off the pace in his only appearances against The Scarlets and The Dragons.
Ian Madigan and John Cooney are beginning to look the part as individuals. It will be interesting to see how they combine in the pressure-cooker environment where time on the ball will be at a premium.
Admittedly, Brendan Macken made a serious impact when introduced against Edinburgh. The man of the match award was pushing more than a little for a player showing slow, steady progress.
The presence of Brian O'Driscoll last Saturday and Gordon D'Arcy tonight, along with Isa Nacewa, Fergus McFadden and Kearney, should pour confidence into Macken opposite his Ireland U20 colleague Eoin Griffin.
Connacht coach Eric Elwood gives a debut to veteran goal-kicking machine Scotland fly-half Dan Parks in a bid to turn those narrow defeats into glorious victories.
He has also made the interesting choice of going for Academy first year apprentice Robbie Henshaw, more naturally a centre, at full back for injured captain Gavin Duffy on his second start.
Former Waikato captain Nathan White will take over the captain's armband and he will be determined to make a strong impression against the club he played for last season.
Connacht have lost nine out of their last 10 against Irish provinces. But they will know Leinster are coming with a callow forward eight and inexperience at half-back.
While Leinster have not quite hit their high standards yet, they have pocketed three successive wins.
Schmidt will be keen for them to repeat their clean sweep of six straight wins against their Irish provincial rivals last season in the League.
Connacht: R Henshaw; T O'Halloran, E Griffin, D McSharry, F Vainikolo; D Parks, K Marmion; D Buckley, A Flavin, N White (capt), M Swift, M McCarthy, E McKeon, J O'Connor, G Naoupu.
Leinster: R Kearney; F McFadden, B Macken, G D'Arcy, I Nacewa; I Madigan, J Cooney; H van der Merwe, T Sexton, J Hagan, Q Roux, T Denton, B Marshall, S Jennings (capt), L Auva'a.