There is a similar swing of fortunes in prospect at Murrayfield where fourth plays fifth when Cardiff Blues travel to the capital city to face Edinburgh on Friday night. A win is vital for the home side if they are to continue their recent good form and mount a late challenge for the title.
Also on Friday night, Connacht will be looking to rewrite over 20 years of history and claim a success against third-placed Munster who, with a game in hand over the leaders, are still in the running for two trophies this season - the Magners League and Heineken Cup.
Friday's third game will see the Ospreys and Ulster meeting for the fourth time this season. An Ulster victory will make it honours shared and keep them clear of the bottom of the table.
Finally, in Wales on Sunday, victory could see the Newport Gwent Dragons overtake their visitors, Glasgow Warriors, and, depending on results elsewhere, further their European ambitions by elevating them to be the third-placed Welsh team.
MAGNERS LEAGUE - ROUND 14 FIXTURES:
Friday, March 28 -
Ospreys v Ulster, Liberty Stadium, 7.10pm (live Setanta Sports Ireland/BBC Sport Wales)
Connacht v Munster, The Sportsground, 7.30pm (live Setanta Sports 2/deferred coverage Setanta Sports Ireland)
Edinburgh v Cardiff Blues, Murrayfield, 7.30pm
Saturday, March 29 -
Llanelli Scarlets v Leinster, Stradey Park, 5.30pm (live Setanta Sports 2/S4C/deferred coverage Setanta Sports Ireland)
Sunday, March 30 -
Newport Gwent Dragons v Glasgow Warriors, Rodney Parade, 4.05pm