Saracens mounted a late push but were unable to avoid losing to Exeter Chiefs at Sandy Park.
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.
It was a miserable Boxing Day for the Ospreys, as they were hammered by the Scarlets, while Cardiff Blues won the other Welsh derby.
Bordeaux went above Lyon to rise to the Top 14 summit after beating La Rochelle, while All Blacks great Ben Smith saw red on...
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Bath arrived at the Madejski Stadium with no form to speak of, but Stuart Hooper's side stormed to a comprehensive win against London Irish.
George Turner's late try ensured Glasgow Warriors claimed the bragging rights in their 1872 Cup clash with Edinburgh in the Pro14.
Handre Pollard missed some crucial kicks on his Montpellier debut while Top 14 leaders Lyon
Saracens won a fifth straight Premiership match, though they are still far behind Leicester Tigers, who were defeated by Exeter Chiefs.
Five tries from the 60th minute onwards gave Gloucester just their second win in eight matches in all competitions.
Pro14's Conference A leaders Leinster dismantled second-placed Ulster on Friday, scoring eight times before the beaten visitors rallied.
Brothers Joe and Sam Simmonds were influential as Exeter Chiefs moved to the brink of a quarter-final spot in Europe.
Brothers Billy and Mako Vunipola played starring roles as reigning champions Saracens defeated Munster in the European Champions Cup.
Juan Imhoff scored two of Racing 92's six tries as they beat Ospreys 40-27 to increase their lead at the top of Pool 4.