Defending Ulster Bank League champions Lansdowne ran out comfortable winners over Young Munster on the opening Saturday of the season.
Newly promoted Galwegians and Garryowen recorded opening day victories over Cork Con and Ballynahinch respectively, while Old Belvedere and Clontarf also both won.
Galwegians 12 Cork Consitution 11, Crowley Park
Scorers: Galwegians: Tries: Cormac Brennan, Ed O'Keeffe; Con: Aidan Moynihan
Cork Constitution: Try: Rob Jermyn; Pens: Tomas Quinlan 2
HT: Galwegians 7 Cork Constitution 6
New backs Cormac Brennan and Ed O'Keeffe both touched down as Galwegians enjoyed a winning return to Division 1A at the expense of Cork Constitution.
Brennan stormed through midfield for a third-minute converted try at Crowley Park. 'Wegians indiscipline allowed Cork Con out-half Tomas Quinlan to make it a one-point game by half-time.
A quick turnover from a lineout and slick hands then put winger O'Keeffe over in the corner in the 58th minute. After 'Wegians lost replacement hooker Juan Anaya to the sin-bin, Constitution responded with a late unconverted effort from winger Rob Jermyn but the home side deservedly held on.
Garryowen 14 Ballynahinch 10, Dooradoyle
Scorers: Garryowen: Try: Shane Buckley; Pens: James Frawley 3
Ballynahinch: Try: Jordan Grattan; Con: Chris Quinn; Pen: Chris Quinn
HT: Garryowen 3 Ballynahinch 3
Garryowen joined fellow promoted side Galwegians in getting off to a positive start in the top flight, with right winger James Frawley booting them past Ballynahinch on a 14-10 scoreline.
This was a typically error-strewn early season affair at Dooradoyle, and Garryowen player-coach Conan Doyle handed league debuts to three U20 players - Ed Barry, Jay Kavanagh and Elliott Fitzgerald.
Chris Quinn and Frawley kicked a penalty apiece during a defence-dominated first half, and the Light Blues gained crucial momentum thanks to Frawley penalties after 46 and 47 minutes and a Shane Buckley try with 12 minutes left. Jordan Grattan's late try earned a bonus point for 'Hinch.
Lansdowne 29 Young Munster 6, Aviva Stadium
Scorers: Lansdowne: Tries: Tom Farrell, Ross Deacon, Penalty try, Tom Daly; Cons: Scott Deasy 3; Pen: Scott Deasy
Young Munster: Pen: Paul Downes; Drop: Paul Downes
HT: Lansdowne 3 Young Munster 6
Centre pair Tom Farrell and Tom Daly starred behind a dominant scrum as Lansdowne began their Division 1A title defence with a 29-6 bonus point victory over Young Munster.
A drop goal and penalty from out-half Paul Downes gave Munsters a 6-3 interval lead at the Aviva Stadium in what was a repeat of last year's semi-final. Lansdowne needed an extra-time try to win that contest, but today they cantered clear of the Limerick men with four second half touchdowns.
The fleet-footed Farrell finished a brilliant breakaway try from his own 22, number 8 Ross Deacon scored a pushover effort, and the hosts' scrum earned them a penalty try before Daly, the Ireland Sevens captain, touched down from an intercept.
Old Belvedere 27 Terenure College 8, Anglesea Road
Scorers: Old Belvedere: Tries: Penalty try, Daniel Riordan, Ed Rossiter; Cons: Shane McDonald 3; Pens: Shane McDonald 2
Terenure College: Try: Robert Duke; Pen: Stephen O'Neill
HT: Old Belvedere 13 Terenure College 8
On Friday Old Belvedere gave Terenure College a 27-8 beating at Anglesea Road. Belvo mastered the tricky conditions with a penalty try giving them a 13-8 interval lead, and new signing Ed Rossiter, the ex-Garryowen hooker, and full-back Daniel Riordan both touched down in the second half.
UCD 16 Clontarf 24, Belfield Bowl
Scorers: UCD: Try: Brian Cawley; Con: Conall Doherty; Pens: Conall Doherty 3
Clontarf: Tries: Mick McGrath 2; Con: Joey Carbery; Pens: Joey Carbery 4
HT: UCD 6 Clontarf 11
Mick McGrath bagged a brace of tries as last season's beaten finalists Clontarf opened their campaign with a 24-16 away win over UCD on Friday night.
The Leinster winger scored in each half at a very wet Belfield Bowl as 'Tarf edged out the students in an entertaining Division 1A opener.
Ireland under-20 international Joey Carbery, who switched from UCD to Clontarf in the summer, came back to haunt his former side with an 11-point kicking contribution.
Ballymena 27 Belfast Harlequins 23, Eaton Park
Scorers: Ballymena: Tries: Martin Irwin, Callum Patterson, David Whann; Cons: Ritchie McMaster 3; Pens: Ritchie McMaster 2
Belfast Harlequins: Tries: Barry Monaghan, David McMaster 2; Con: Mark Best; Pens: Mark Best 2
HT: Ballymena 20 Belfast Harlequins 13
Determined defence late on saw Ballymena take the Ulster derby spoils as they edged out Belfast Harlequins 27-23 at Eaton Park.
Impressive young lock David Whann ran in a tremendous 58th-minute solo try which proved to be the match-winning score, as Harlequins were unable to respond in a frenetic final quarter.
Callum Patterson chased down his own kick through to score a try that had the Braidmen 20-13 to the good at half-time, adding to an initial touchdown from his centre partner Martin Irwin. Barry Monaghan's second half try, adding to an earlier double from David McMaster, had 'Quins back in front until Whann had the final say.
Buccaneers 21 Shannon 11, Dubarry Park
Scorers: Buccaneers: Tries: Alan Gaughan, Rory O'Connor; Con: Conor McKeon; Pens: Conor McKeon 3
Shannon: Try: Shane Mullaney; Pens: Ronan McKenna 2
HT: Buccaneers 8 Shannon 3
Brett Wilkinson won this battle of the former props-turned-head coaches as his Buccaneers side beat Marcus Horan's Shannon by 10 points at Dubarry Park.
A try from experienced centre Alan Gaughan split the sides the break - 8-3 - and Buccs took control of the second half playing into the wind. Connacht Academy out-half Conor McKeon, who has switched from Lansdowne, landed his second penalty before winger Rory O'Connor broke out wide, chipped over the cover and won the race for the touchdown.
McKeon converted and swapped penalties with Ronan McKenna, while a late Shannon rally saw centre Shane Mullaney cross the whitewash.
St Marys College 46 Dolphin 10, Templeville Road
Scorers: St. Mary's College: Tries: Darragh Fanning 3, Marcus O'Driscoll, Mark Fallon, Ray Crotty, David Fanagan; Cons: Sean Kearns 4; Pen: Sean Kearns
Dolphin: Try: John Madigan; Con: Cian McGovern; Pen: Cian McGovern
HT: St. Mary's College 22 Dolphin 10
Darragh Fanning was in sizzling form for St Mary's College as he scored three of their seven tries in a 46-10 thrashing of a disappointing Dolphin side.
The Leinster winger thrilled the Templeville Road faithful with two quick-fire scores early on, and it was his inviting pass that put centre Marcus O'Driscoll in under the posts for try number three. Recent Munster cap John Madigan replied for Dolphin before half-time.
But it was one-way traffic over the closing 40 minutes. Man-of-the-match Fanning completed his hat-trick, number 8 Mark Fallon got over in the corner and full-back Ray Crotty and scrum half David Fanagan got in on the scoring act late on.
UL Bohemians 5 Old Wesley 33, Annacotty
Scorers: UL Bohemians: Try: Darren Moroney
Old Wesley: Tries: Craig Telford, Barry McLaughlin, Ian Cassidy, Josh Hinde; Cons: Barry McLaughlin 2; Pens: Barry McLaughlin 3
HT: UL Bohemians 5 Old Wesley 14
Last year's Division 2A champions Old Wesley announced themselves in the second tier with a terrific bonus-point triumph over UL Bohemians at Annacotty. A first half try from in-form centre Darren Moroney proved to be Bohs' only score.
Morgan Lennon's Wesley side built a 14-5 half-time advantage as Craig Telford went over from close range and goal-kicking winger Barry McLaughlin landed three successful penalties.
The Dubliners' turned on the pace and power with McLaughlin finishing with 18 points, including a try, two conversions and a penalty, and captain Ian Cassidy and busy lock Josh Hinde also dotting down.
Blackrock College 11 Dublin University 10, Stradbrook
Scorers: Blackrock College: Try: Mikey Russell; Pens: Peter Quirke, David Scott-Lennon
Dublin University: Try: Raef Tyrrell; Con: Conor Kearns; Pen: Conor Kearns
HT: Blackrock College 3 Dublin University 7
On Friday, Blackrock College, promoted from Division 2A last season, enjoyed a nail-biting 11-10 victory over Dublin University in Division 1B. Full-back David Scott-Lennon's late penalty saw them prevail at rain-soaked Stradbrook.