Former Munster lock Brian Hayes scored his third try in as many games as Cork Constitution toppled Division 1A leaders Lansdowne 25-20 on the Aviva Stadium's back pitch.
The gap between the clubs in the Division 1A table - Cork Con remain third overall - is now just four points after the Leesiders outscored the headquarters side by three tries to two, including a terrific intercept score from hooker Max Abbott.
Four second-half tries saw Clontarf hand Garryowen a 39-10 beating and move into second place. Centre Matt D'Arcy is one of five 'Tarf players in the Ireland Club international squad to play England Counties on Friday.
Promising UCD out-half Matthew Gilsenan kicked 12 points as he got one over on his older brother Conor, who was part of the St Mary's side that was beaten 32-18 by the students.
The basement battle at Lakelands went the way of Terenure College, full-back Jake Swaine touching down and kicking nine points in a 24-20 win over bottom side Old Belvedere.
Bryan Mollen's 77th-minute penalty guided Dublin University to a famous 15-12 success against Young Munster in Greenfields. Forwards Tom Ryan and Pierce Dargan scored a try each in the first half.
Meanwhile, UCC claimed the result of the weekend in Division 1B as they ended Buccaneers' 13-match unbeaten run. Winger Kevin O'Keeffe starred in a nail-biting 13-12 triumph, kicking two penalties and running in a first-half try.
Former Leinster underage player David Poff bagged a brace of tries as Old Wesley overcame Ballynahinch 28-14 at Ballymacarn Park, with the bonus-point win giving them an eight-point cushion in fourth place.
Johne Murphy's Naas are also on course to reach the promotion play-offs. Versatile back Peter Osborne celebrated his Ireland Club International call-up with a try and three conversions in their 21-14 victory at home to Shannon.
Dolphin's bid to avoid relegation received a huge boost when they edged out Ballymena 18-16 at Irish Independent Park. Ryan Murphy's sixth try of the campaign and two drop goals from Barry Keeshan completed a thrilling comeback for the Corkmen.