Ospreys opened their Heineken Cup campaign with a 38-17 bonus-point win over Treviso at the Liberty Stadium but only after snuffing out a spirited second-half comeback by the Italians.
The Welsh region were indebted to a tries from Eli Walker, Hanno Dirksen (2) and Ashley Beck, while 18 points came from the boot of outside-half Dan Biggar.
Treviso scored two tries through Manoa Vosawai and Luke McLean, while Kris Burton supplied seven points with the boot.
Last season's beaten finalists Ulster opened their Heineken Cup campaign with maximum points thanks to Ruan Pienaar's dramatic bonus try.
The newly-returned Pienaar got down under the posts after Ulster had broken out of their 22 in injury time with the last move of the game.
Ulster's other tries came from Paul Marshall (2) and Andrew Trimble, with Paddy Jackson making a vital contribution of 21 points from the boot on a pulsating night for new Ulster coach Mark Anscombe's side.