In Division 1B, Instonians and Garryowen produced dramatic comebacks, while Blackrock College and Highfield secured narrow victories. Elsewhere, Corinthians kept UL Bohemian scoreless in Division 2A, Bective Rangers ran riot against Buccaneers in Division 2B South, and several closely contested encounters added to another eventful weekend across the league.
Old Belvedere secured an important 11-7 victory over Clontarf at Ollie Campbell Park to move top of Division 1A, with replacement George Hadden's second half try proving decisive.
Sam Wisniewski kicked penalties in the 9th and 23rd minutes to establish an early advantage, but Clontarf responded through Dylan Donnellan, whose 26th minute try was converted by Conor Kelly to give the visitors a 7-6 half-time lead.
The contest remained finely balanced until Hadden crossed in the 61st minute, putting Belvedere back in front. The hosts defended their narrow advantage throughout the closing stages to claim a four-point victory.
Ballynahinch held off a determined Lansdowne fightback to secure a 21-17 victory at Ballymacarn Park.
Juan Beukes gave Lansdowne the perfect start with a sixth minute try, but Conor Rankin responded with two penalties before Ryan Connolly crossed for Ballynahinch in the 21st minute.
Rankin converted and added another penalty before half-time to establish a 16-5 advantage. Captain Claytan Milligan extended the lead with a try in the 65th minute, but Lansdowne finished strongly.
Daniel Hurley crossed with five minutes remaining before Beukes completed his double in stoppage time. Michael Moloney converted the final try, but Ballynahinch held on for victory.
Old Wesley produced an impressive attacking display to defeat Young Munster 26-7 at Energia Park.
Matias Jensen opened the scoring after just four minutes before Paidi Farrell added another try midway through the opening half. Tom Larke converted both scores to give Wesley a 14-0 advantage.
Liam McMahon responded for Young Munster shortly before the interval, with Benn Dalle Cort converting, but the hosts dominated the second half. Replacement Rian Handley crossed on the hour mark before Liam Grover secured the bonus point with a fourth try in the 75th minute.
Terenure College edged St Mary's College 17-12 at Templeville Road in another closely contested Dublin derby.
Michael McCormack opened the scoring for Mary's in the 25th minute, but Terenure responded through replacement Bryan O'Connor before Peter Sylvester added another try in first-half stoppage time.
Aaron O'Sullivan crossed for Mary's before the interval, leaving Terenure narrowly ahead at 14-12. Aran Egan's 55th-minute penalty proved the only score of the second half.
UCD secured an 18-13 victory over Cork Constitution at the UCD Bowl, with Charlie Molony crossing after just four minutes.
Billy Scannell responded for Cork Con before Aidan Moynihan's penalty gave the visitors an 8-7 interval advantage.
Maxim Aschenbrenner restored UCD's lead with a try in the 49th minute, while Paddy Clancy added two penalties. Bobby O'Callaghan crossed late for Cork Con, but the students held firm.
In Division 1B, Instonians produced one of the weekend's most dramatic comebacks, defeating Naas 32-27 at Shaw's Bridge.
Naas raced into an early lead through tries from Tadhg Brophy, Paddy Taylor and captain Ryan Casey, but Liam Kaprigiannis and Oli Clark responded to leave Instonians trailing 20-15 at half-time.
Muiris Cleary extended Naas' advantage shortly after the restart, but Clark completed his double before replacement Jack Parkinson crossed in the 69th minute.
Bevan Prinsloo then delivered the decisive moment, touching down three minutes into stoppage time to complete a remarkable five-try victory.
Blackrock College edged City of Armagh 19-17 at Stradbrook, with Barry Galvin and Emmet Burns establishing an early 14-0 advantage.
Armagh responded through Shea O'Brien and Ethan Graham to reduce the deficit to two points at half-time.
Derry Moloney crossed for Blackrock in the 55th minute before Nathan Hamilton replied six minutes later, but the hosts held on.
Dublin University recorded a convincing 29-7 victory over Nenagh Ormond at College Park.
James Browne, captain Hugo Lynch, Callum McDonald and Jonathon Ginnety all crossed during a dominant first half as Trinity established a 26-0 interval advantage.
Matthew Burke replied for Nenagh shortly after the restart, but Conor Tracey's second-half penalty completed the scoring.
Highfield secured a narrow 17-15 victory over MU Barnhall at Parsonstown, with replacement Conor Galvin scoring twice.
Shane Mallon and Cathal Duff crossed for Barnhall, who led 12-10 at half-time, before Oisin O'Neill extended their advantage with a penalty.
However, Galvin's second try in the 54th minute, converted by Shane O'Riordan, proved decisive.
Garryowen produced another dramatic comeback, defeating UCC 25-23 at the Mardyke.
Ronan Byrd scored twice for the students, while Gene O'Leary Kareem also crossed and contributed eight points with the boot.
Joe Finn and Blayze Molloy replied for Garryowen before a 76th minute penalty try completed the visitors' turnaround.
In Division 2A, Ballymena overturned a 12-3 half-time deficit to defeat Galwegians 17-12 at Crowley Park.
Tom Gormley and Duinn Maguire crossed for the hosts before James McClean and Angus Graham scored within five minutes of each other after the restart. James McMillan converted both tries to secure the comeback victory.
Dungannon defeated Shannon 14-9 at Stevenson Park, with first-half tries from captain James McMahon and Blake Redmond proving decisive. Shannon responded through three penalties but could not overturn the deficit.
Greystones secured a 17-7 victory over Queen's University, with Jack Barr and Johan van der Flier crossing during the opening half. Gavin Rochford added seven points, while Clark Logan scored Queen's only try in stoppage time.
Corinthians defeated UL Bohemian 19-0, with Aidan Vetjens, Mark Boyle and Colm de Buitlear crossing as the visitors kept their opponents scoreless.
Wanderers recorded a 29-10 bonus-point victory over Cashel, with Matthew Sherwin and replacement Karl Madden crossing before late tries from Dan Carroll and Mark O'Reilly secured the result.
In Division 2B North, Banbridge edged Enniskillen 18-17 at Rifle Park, with Zac Solomon's 74th-minute try overturning the visitors' late advantage.
Malahide defeated Sligo 23-10, with Billy Stanbridge and Payton Jackson crossing and David O'Halloran adding 13 points.
Navan overcame Ballyclare 13-8 through early tries from Ewan Groenewald and Fionn Craik, while Malone defeated Rainey 15-10, with Sam Green and Tane Hotham touching down.
Clogher Valley secured a 24-19 victory over Skerries, with captain Callum Smyton scoring twice before David Stinson added a crucial late try.
In Division 2B South, Bective Rangers produced the biggest winning margin of the round, defeating Buccaneers 59-7 at Dubarry Park.
The visitors ran in nine tries, with Matthew Gilsenan completing a double and David Fitzgibbon converting seven scores.
Midleton also impressed with a 46-7 victory over Monkstown, as captain JB Du Toit completed a hat-trick in a seven-try performance.
Old Crescent defeated Enniscorthy 26-0, securing the bonus point through tries from John Lyons, Joe Rickard, Bailey Faloon and Oisin Toland.
Clonmel overcame Thomond 27-10, with Jason Monua scoring twice alongside tries from Michael Connellan and AJ Thomas.
Bruff held off Dolphin 19-15 at Kilballyowen Park, with tries from Sam Hacket, Jesse Smith and Mark Kennedy establishing a 19-10 half-time advantage. Dolphin responded through Liam Ormond and Fionn Herlihy, but Bruff defended their four-point lead to secure victory.