Four teams from three countries will take a shot at knocking Munster off their perch starting with Leinster-Connacht in Dublin on Friday night, the first of several all-Irish affairs evoking memories over the festive period of Ireland's old inter-provincial championship.
Leinster will go top, at least temporarily, if they take all five points, a big IF made bigger still by the fact that their opponents are not in the habit of leaking tries. They have given away four or more just once this season, to the Warriors in Glasgow in September.
Take that out of the equation and Connacht have conceded a mere eight tries in eight PRO12 matches, thereby restricting the worst of habits - lining up behind their own line for a conversion - to one per game.
Nor are Leinster exactly flush in the try department, having managed one over the course of their two Champions Cup ties against Harlequins and none when they were last on PRO12 duty at the RDS, relying on six penalties shared between Ian Madigan and Jimmy Gopperth to see the Ospreys off.
In spite of that, Leinster have won more try-bonus points this season, four, than anyone else in the Guinness PRO12 - due reward for having scored the most tries, 25.
The last time they managed four in one afternoon, against Benetton Treviso in late November, it was to deny the Italians their first win of a troubled season as well as arguably the upset of the domestic year.
The defending champions will not need to be reminded that they have yet to manage as much as one try against Connacht this season. In Galway at the end of September, they were undone 10-9 with Kieran Marmion accounting for the only try of the match in front of 6,000 at the Sports Ground.
Connacht make the journey across Ireland from west to east reinforced by a run of four straight wins, including the European Challenge Cup double over Bayonne. The victory in France last Saturday underlined the province's success in producing home-grown talent.
No fewer than five Connacht academy players made their first starts at Bayonne and one of them, Caolin Blade, stole the show by scoring both his team's tries. The 20-year-old from the village of Monivea in Co Galway could hardly have made a more spectacular start to maintaining the family's scrum-half tradition.
His father, Pat, played there for Monivea as does Caolin's brother, Darren. An international at under-19 level, Blade was not the only one to make a winning debut on a foreign field.
Flanker James Connolly, a 21-year-old from Naas, No.8 Danny Qualter, 22, from Athlone and centre Conor Finn, 23, from Ballinsaloe in Co Galway went with him every step of the way.
So, too, did Finlay Bealham, an Irish-qualified Australian who has propped for Ireland's under-20s. Head coach Pat Lam considered the challenging GUINNESS PRO12 festive schedule and the inevitable crop of injuries in choosing to give youth a fling and his pre-match comment turned out to be prophetic: "We are going there to win and we believe we have the game plan to win this game."
Of all the fixtures facing the top six of the GUINNESS PRO12, Connacht's is probably the most demanding.
After Leinster on Friday, they head north to Belfast on St Stephen's Day/Boxing Day and six days after tangling with Ulster they will be back in Galway hoping to give Munster more than a serious run for their money by beating them - something they have done just once in 24 Celtic League attempts.
The one certainty about Friday night at the RDS is that it will change the pecking order. Connacht's reward for a double over Leinster would hoist them into the play-off zone of the top four while a home win would put the champions second at the very least.
Once the dust settles in Dublin, the stage will be clear on Saturday for two mighty contests featuring the current top four. Munster, their run of seven straight wins broken by the bruising Champions Cup encounters with Clermont, defend their top spot on Clydeside against opponents who find themselves in the same European boat.
After running Toulouse closer at Scotstoun last week than Munster ran Clermont in Limerick the week before, the Warriors now have the opportunity to help themselves to the perfect antidote. A win would put them top, if only for a matter of hours.
Within 60 minutes of the referee blowing no-side in Glasgow, the Ospreys-Ulster clash in Swansea will ensure another change in the kaleidoscopic view of the summit.
A home win in Glasgow would clear the way for the Ospreys to regain pole position. They lost it, along with their winning seven-match start, against Ulster in Belfast in late November, a time when the Welsh region suffered from the loss of their Wales contingent then on Test duty.
Ulster's immediate return to South Wales, six days after their Champions Cup defeat by the Scarlets in Llanelli, will coincide with Dan Lydiate being available after signing a dual WRU-Ospreys contract following his release from Racing Metro.
His new region will be ready to bust a collective gut after a week to reflect on two close-run matches against Racing, the closest of all GUINNESS PRO12 encounters with the French as reflected in an aggregate score of 37-33 in favour of the wealthy Parisians.
The next three rounds of the GUINNESS PRO12, over a period of 15 days, will have a profound effect on the play-offs in May. The festive schedule facing each of the top six will take some predicting:
Munster (1st, 32 pts):
Warriors (away, Saturday), Leinster (home, Boxing Day), Connacht (away, New Year's Day)
Ospreys (2nd, 31 pts):
Ulster (home, Saturday), Scarlets (home, December 27), Scarlets (away, January 3)
Warriors (3rd, 31 pts):
Munster (home, Saturday), Edinburgh (home, December27), Edinburgh (away, January 2)
Ulster (4th, 31 pts):
Ospreys (away, Saturday), Connacht (home, Boxing Day), Leinster (away, January 3)
Leinster (5th, 28 pts):
Connacht (home, Friday), Munster (away, Boxing Day), Ulster (home, January 3)
Connacht (6th, 27 pts):
Leinster (away, Friday), Ulster (away, Boxing Day), Munster (home, January 1)
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