Munster put in a monumental effort, but Leinster's defence refused to buckle at Thomond Park.
There were wins for Lyon and Racing 92 in the Top 14 as Bordeaux-Begles were usurped at the summit.
Northampton Saints defeated Gloucester in a barnstorming contest at Franklin's Gardens, while Sale Sharks overcame Bath in the Premiership.
Wasps claimed their second win of the Premiership season by overcoming Bristol.
Leigh Halfpenny is out of contract at the end of the season, but Scarlets have no intention of letting the Wales international leave.
It was a miserable Boxing Day for the Ospreys, as they were hammered by the Scarlets, while Cardiff Blues won the other Welsh derby.
Liam Williams will return to Pro14 side Scarlets next season after his contract with Premiership champions Saracens comes to an end.
Toulouse safeguarded the future of their France full-back Thomas Ramos as the Top 14 club entered into the festive spirit on Christmas Eve.
Ian Foster's New Zealand coaching staff has been finalised with the appointment of Scarlets boss Brad Mooar, who will head home in June.
Bordeaux went above Lyon to rise to the Top 14 summit after beating La Rochelle, while All Blacks great Ben Smith saw red on his Pau...