Saracens breathed new life into their European Champions Cup title defence as the Vunipola brothers starred in a 15-6 win over Munster at Allianz Park.
The reigning champions, who have lifted the trophy in three of the past four seasons, had won just one of their opening three games and came into the game trailing Pool 4 leaders Racing 92 by 11 points.
They were 6-3 behind against Munster early in the second half when a melee ensued after Jamie George appeared to be enraged by a conversation with a member of Munster's staff.
The brawl spilled over onto the advertising hoardings and, once it had subsided, Munster got a penalty which JJ Hanrahan missed.
Saracens soon came alive as Billy Vunipola, with three men converging on him, flipped a brilliant pass out to Sean Maitland to score before Mako Vunipola dotted down eight minutes from time to leave Sarries just one point behind second-placed Munster.
Leinster, the side Sarries beat in last season's final, made it four wins from four in Pool 1 with a dominant 50-21 victory over Northampton as Garry Ringrose scored a hat-trick.
The Ireland centre went over twice in the opening six minutes before Tadhg Furlong and Dave Kearney earned Leinster a bonus point prior to half-time.
Ringrose completed his treble after James Lowe had scored, with Caelan Doris crossing for Leinster's seventh and final try.
Premiership leaders Northampton - whose try-scorers were Dan Biggar, Ollie Sleightholme and Ahsee Tuala - now trail Leinster by 10 points with two games remaining.
Robin Copeland's 81st-minute try earned Connacht a 27-24 success over Gloucester, while Marco Lazzaroni's late score proved the difference in Benetton Treviso's 25-22 triumph against Lyon.
Toulouse beat Montpellier 26-18 while La Rochelle edged past Glasgow Warriors 12-7.