Reigning RaboDirect PRO12 champions - and current league leaders - Leinster kicked off the weekend with a trip to face Ospreys, losing 25-19 on Friday night.
Dan Biggar kicked 20 points, including a late drop-goal, to ensure the Welsh region claimed four points and preserved their hopes of a top-four finish.
Ulster capitalised on the slip-up and romped to a 58-12 victory over fellow Irish side Connacht to close the gap at the top to four points.
Andrew Trimble scored a hat-trick - three of eight Ulster tries - as Connacht, who came into the game in good form, were brushed to one side.
The win also saw Ulster move beyond Munster and into second, something Rob Penney's side failed to correct on Saturday when they hosted Glasgow Warriors.
Fourth-placed Warriors maintained their four-point gap to Ospreys back in fifth by inflicting Munster's first home RaboDirect PRO12 defeat of the campaign.
Sean Maitland, Jonny Gray and man-of-the-match Josh Strauss dotted down for the visitors, who picked up a fourth league win on the bounce.
Elsewhere there was an eye-catching win for Benetton Treviso, who ran in five tries to beat Newport Gwent Dragons and move within just two points of the Welsh side.
They also went well clear of fellow Italians Zebre, who scored three tries at Scarlets but ultimately lost 27-20, at the foot of the table.
And a resurgent Cardiff Blues claimed their second RaboDirect PRO12 win on the trot, following last month's victory over Ulster with a 29-22 win at Edinburgh - courtesy of Dafydd Hewitt's late try.
TRY OF THE WEEKEND
With eight Ulster tries to pick from, each of Trimble's three scores are worth a second looks - including an 80-metre sprint up the right touchline.
However, Luke Marshall's second-half effort was the pick of the bunch in no small part due to a piece of magic from an out-of-position Tommy Bowe.
Bowe - wearing No.13 - received the ball from Paddy Jackson and, with a pair of defenders approaching, produced a superb offload back into the arms of the fly-half.
It sent Jackson into space and Marshall was waiting on his shoulder to cross over and further punish Connacht.
BREAK OF THE WEEKEND
Munster only managed five points at Thomond Park on Saturday but they weren't bad - thanks largely due to a smart break near halfway.
Conor Murray fed JJ Hanrahan, whose short pass found James Downey under instant pressure from a handful of Warriors.
However, the centre didn't panic and popped the ball to the onrushing Simon Zebo, dashing through the line and towards the posts.
The winger was eventually wrestled to the ground but Munster recycled the ball and CJ Stander was waiting to score in the corner.
PLAY OF THE WEEKEND
Treviso put in a superb performance when the Dragons came to visit and they set the tone halfway through the first half.
At 6-3 down the Italians had their visitors pegged back in their own 22 and after Newport tried and failed to run the ball out of trouble, Dan Evans looked to boot clear.
However, Treviso were organised and efficient and with their line fast-approaching Evans took too long, as Robert Barbieri engulfed the clearance with an imposing charge-down.
The No.8 composed himself, collected the loose ball and fed Ludovico Nitoglia for the first of Treviso's five tries.
PLAYER OF THE WEEKEND
Trimble was quite simply everywhere on Friday night, running in three tries of his own and laying on two more for his teammates.
The Ireland winger's showreel included an 80-metre dash for the line and a great piece of improvisation, sending a quick lineout to Paul Marshall inside the Treviso half for one of the scrum-half's two tries.
After an excellent two months with Ireland, the 29-year-old looks primed to lead Ulster's push for the RaboDirect PRO12 title.
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