Lansdowne still look the team to beat in Division 1A of the Ulster Bank League after beating Young Munster at Tom Clifford Park for the first time since 2011.
Meanwhile, defending champions Cork Constitution have leapfrogged Terenure College in pursuit of the second home semi-final berth.
Wingers Luke Fitzgerald and Conor Hayes both touched down for four-try Munsters, but it wasn't enough to deny Lansdowne, who won 27-24.
Buccaneers' relegation was confirmed by their 22-10 loss at home to fourth-placed Garryowen. It was a first Dubarry Park run-out of the season for Ireland Sevens flyer Jordan Conroy who delivered a 20th-minute try, but scores from Tim Ferguson and in-form Ireland U-20 hooker Diarmuid Barron (2) gave the Light Blues the win.
Tomas Quinlan's kicking haul of 15 points ensured Cork Con won 30-27 at home to play-off rivals 'Nure. The sides are level on 56 points, with second-placed Con, who travel to Clontarf in next Saturday's final round, ahead on scoring difference.
St Mary's College, whose Division 1A status now hinges on the relegation/promotion play-offs, went down 45-30 to a Clontarf side who are locked in a three-way battle for fourth place.
Shannon are 80 minutes away from winning the Division 1B title and promotion after they overcame Old Belvedere 12-7.
Ballynahinch were knocked off the summit by Shannon after their 14-14 draw with Old Wesley; Conall Boomer's try bringing 'Hinch level but Richard Reaney missed the conversion.
In the final round of regular-season games in the Women's All-Ireland League, leaders UL Bohemian were merciless in their 78-0 win at home to Tullamore.
The bottom-placed Midlanders were no match for Bohs, who reaffirmed their status as favourites to win the competition.
Bohs will face fourth-placed Cooke in a home semi-final in Limerick, after the Belfast side went down 10-5 away to Old Belvedere, whose reward for a third-place finish is local derby at Railway Union, who thrashed Galwegians 64-0 at home.
Both semi-finals take place next Saturday.