The Scarlets moved into sixth spot in the PRO12 after a bonus-point victory over the Dragons at the Millennium Stadium.
Munster maintained their challenge for a home Guinness PRO12 semi-final with a 30-19 victory over Benetton Treviso.
Dan Biggar stole the show as the Ospreys sent Cardiff Blues crashing to a 31-23 defeat at the Millennium Stadium.
Glasgow Warriors' clinical finishing proved too much for Connacht as they ran out 31-13 bonus-point winners in Galway.
Edinburgh kept their top-six hopes alive with a 37-0 hammering of Guinness PRO12 strugglers Zebre at Murrayfield.
Ulster secured their place in the Guinness PRO12 semi-finals with a 26-10 victory over Leinster at Kingspan Stadium.
Second row Rynard Landman will captain the Dragons in their Guinness PRO12 derby with Scarlets at Millennium Stadium.
Wales international Gethin Jenkins is back to skipper the Cardiff Blues in their PRO12 derby at the Millennium Stadium.
Connacht have made three changes in preparation for their Guinness PRO12 game against league leaders Glasgow.
Munster host Treviso at Irish Independent Park looking to keep the pressure up on Guinness PRO12 leaders Glasgow.
Edinburgh will be looking take their European success into the PRO12 when they host Zebre on Friday.
Jamie Heaslip makes his 200th appearance for Leinster as his side takes on Ulster in the Guinness PRO12 on Friday night.