Stephen O'Neill's first-half try was the difference between the teams at Lakelands Park as Terenure College continued their dream start to life in Division 1A with a 14-9 win over defending champions Clontarf.
Terenure's fifth victory of the campaign extended their winning streak in the Ulster Bank League to an incredible 28 games, and in the process dented Clontarf's title defence with a second defeat.
The hosts went ahead thanks to two James Thornton penalties. A 37th-minute try by O'Neill (below) from a kick through made it 11-0 at half-time.
Improving 'Tarf finally opened their account with a 54th-minute penalty from replacement Alan Hughes, before a strong break by Connacht loanee John Cooney paved the way for Thornton's third penalty, 13 minutes from time.
Hughes responded with his second and third penalties to make life difficult for James Blaney's men once again but despite their best endeavours, 'Tarf had to be content with a losing bonus point.
Ballynahinch are now fourth in the table after a brilliant final-quarter effort against St Mary's College saw them run out 33-13 bonus point winners at a rain-soaked Ballymacarn Park.
Trailing 13-6 approaching the hour mark, Derek Suffern's side produced a terrific turnaround with 18-point centre Richard Reaney, Ross Adair and Robin Harte all touching down, and the bonus point secured by a 78th-minute penalty try.
Ben Martin's 68th-minute penalty made it back-to-back wins for Young Munster as they edged out Cork Constitution 9-6 at Temple Hill.
Dolphin avoided defeat for the first time in this season's league with a deserved 22-22 draw with Old Belvedere at Anglesea Road. The levelling score was a last-minute penalty from ex-Old Christians scrum-half Stuart Lee.
Ireland U-20 out-half Ross Byrne contributed a try and three penalties as UCD won 19-10 on the Aviva Stadium's back pitch to condemn Lansdowne to their second successive defeat.
Meanwhile, Ballymena are the new leaders in Division 1B after beating former front-runners Galwegians 23-22 at a wet Crowley Park.
The Braidmen picked up their fifth and most significant win of the season despite being outscored by four tries to two. In the end, an excellent injury-time penalty from replacement Tim Small, struck from the 10-metre line, split the sides.
Dublin University's resurgence continued as they came away from Dooradoyle with a 14-8 triumph over Garryowen.
Jack McDermott kicked three penalties and winger Tim Maupin, who is part of the USA's November tour squad, claimed a try.
Malone gained their second victory with a 23-10 dismissal of UL Bohemians at Gibson Park. Their 20-point first half included a brace of tries from impressive scrum-half John Creighton.
Belfast Harlequins held off a late Shannon surge to win 26-21 at Thomond Park. Quins centre Eamon Lane took his league tally to 46 points as he kicked four penalties and converted tries from Caleb Montgomery and Peter Dunlop.
In Friday's Connacht derby at Dubarry Park, second-half tries from Eoghan Masterson and Pat O'Toole saw Corinthians stun error-strewn hosts Buccaneers 14-10.
Niall Scannell (Dolphin): The Munster hooker continued his return from a length lay-off as he scored a crucial try in his side's thrilling 22-22 draw with Old Belvedere.
Dolphin are still without a league win but Saturday's draw did at least stop their four-game losing run.
One to Watch
Stephen O'Neill (Terenure College): The young centre's first-half try proved decisive as Terenure made a huge statement of intent by beating defending champions Clontarf.
O'Neill has started the season in fine form and if the Leinster U-20 star continues to shine, he could well in be line for a call-up the Blues' British & Irish Cup squad.
Number of the weekend
28: Terenure's incredible winning streak in the league was extended as they opened up a seven-point lead at the top of the table.
'Nure were beaten by UCD in the Leinster Senior Cup three weeks ago but showed no ill effects of that defeat as they continued their unbeaten run to a staggering 28 games.