Ryan Baird and Dave Kearney both scored hat-tricks as Conference A leaders Leinster routed Glasgow Warriors on Friday.
Josh Adams will miss the games against England and Scotland as he requires surgery on the ankle he injured against France.
Southern Kings and Benetton Treviso both fell short on Welsh soil as Scarlets and Cardiff Blues earned Pro14 wins.
The Ospreys claimed only their second Pro14 win over the season at the expense of high-flying Ulster in a stormy Swansea.
Ulster maintained their unbeaten home record in the Pro14 with an emphatic win over Munster, who slipped off the top of Conference B.
It was a miserable Boxing Day for the Ospreys, as they were hammered by the Scarlets, while Cardiff Blues won the other Welsh derby.
Wales scrum-half Tomos Williams was an usher at his brother's wedding and returned to celebrate after playing in Cardiff's derby win.
George Turner's late try ensured Glasgow Warriors claimed the bragging rights in their 1872 Cup clash with Edinburgh in the Pro14.
Having beaten Glasgow Warriors in the Pro14 final in May, Leinster were victorious again at Scotstoun as Cian Kelleher scored a brace.
Munster were delighted to have Andrew Conway back in Pro14 action as he settled an all-Irish affair with Ulster.