Leinster became the first Pro14 side to win their first 12 league matches of a season after they overcame Ospreys on Friday.
It was a record-breaking outing for Munster in Pro14 action on Friday, while Glasgow Warriors were also big winners.
At the end of another week of crisis, Saracens had rare cause for cheer as they reached the quarter-finals of the European Champions Cup.
A thrashing of Lyon ensured Leinster made it five wins from five in the European Champions Cup, while Racing 92 reached the last eight.
Joey Carbery has suffered another injury blow and will play no part in Ireland's bid to regain the Six Nations title.
Ulster maintained their unbeaten home record in the Pro14 with an emphatic win over Munster, who slipped off the top of Conference B.
George Turner's late try ensured Glasgow Warriors claimed the bragging rights in their 1872 Cup clash with Edinburgh in the Pro14.
Saracens claim a derogatory comment made to Jamie George by Munster's chief medic sparked a fracas at Allianz Park.
Brothers Billy and Mako Vunipola played starring roles as reigning champions Saracens defeated Munster in the European Champions Cup.
There were seven tries in Leinster's 43-16 European Champions Cup win over Northampton Saints as they made it 10 victories from 10.