Zebre handed Ulster a shock first defeat of the Pro14 season to extend their winning run, while Munster were lifted by their returning Lions as they saw off Cardiff Blues.
Ulster's defeat means Glasgow Warriors are the only remaining unbeaten team this season, the Irish side going down to a spirited Zebre, who are making strides under former Edinburgh and Connacht boss Michael Bradley.
Zebre beat Southern Kings last week, running in six tries in a bonus-point hammering, but they showed a steelier side here, fighting back from 13-6 down at the break to win 27-23.
Giovanni Licata and Mattia Bellini touched down to turn around the half-time deficit, with Renato Giammarioli intercepting a Christian Lealiifano pass to go the length of the field as the Ulstermen were threatening a comeback of their own.
Though they picked up a losing bonus point, Ulster are third in Group B, behind Scarlets and Leinster.
Also in their pool, Dragons secured a second win of the campaign against the Kings, who remain without a point to their name in a miserable introduction to the league.
Munster had gone down to Glasgow last week, but they responded in style to ease by Cardiff 39-16.
British and Irish Lions Conor Murray, Peter O'Mahony and CJ Stander all made their first appearances of the campaign, with Murray scoring the game's first try in the 13th minute to put Munster on the board.
Josh Turnbull's try and a trio of Jarrod Evans penalty goals had the Blues 16-13 up at the break, but Munster ran in 26 unanswered points in the second half, taking advantage of Blues prop Taufa'ao Filise's yellow card to seize control.
John Ryan and JJ Hanrahan crossed as Munster had the man advantage, with Robin Copeland and a second for Hanrahan on his return to Thomond Park sealing the bonus point.