Former Munster lock Brian Hayes scored his third try in as many games as Cork Constitution toppled Lansdowne 25-20 on the Aviva Stadium's back pitch.
The gap between the clubs in the Division 1A table - Constitution remain third overall - is now just four points.
After a penalty miss from Scott Deasy, Lansdowne were held up over the line before their scrum forced a penalty try with 25 minutes on the clock. But Cork Con's forwards knuckled down and following a series of pick and goes, the ball was moved wide for Rob Jermyn to run in an unconverted score.
Chances were at a premium in the third quarter during which Tomás Quinlan sent over a penalty and opposite number Deasy replied. Deasy, the top flight's leading scorer with 145 points before kick-off, increased his influence with a well-struck penalty in the 63rd minute to make it 13-8.
Crucially, last year's runners-up replied within two minutes and in stunning fashion. Hooker Max Abbott intercepted and charged 40 metres to the line before Quinlan converted.
The nip and tuck continued and Ireland Sevens star John O'Donnell finished a breakaway seven-pointer for a 20-15 lead with 10 minutes remaining.
Again, though, Brian Hickey's men hit back. Hayes showed his pace to gallop down the wing and score. Quinlan, again, converted and tagged on a 75th-minute penalty, before a dogged defensive stand saw Constitution hold out to the end.
Elsewhere, Clontarf cut loose at Dooradoyle to run out 39-10 winners over Garryowen and move into second place in Division 1A.
In-form No 8 Michael Noone's try just before half-time saw 'Tarf take a 10-3 lead, with Garryowen captain Neil Cronin swapping penalties with David Joyce.
A converted effort from out-half Dave McCarthy had the Light Blues level in the 48th minute, but the north Dubliners took over, running in four tries in the final half an hour, beginning with talismanic centre Matt D'Arcy's eighth of the campaign.
Out-half Joyce landed a penalty on the hour mark and converted young full-back Jack Power's try five minutes later. Replacement Cian O'Donoghue followed up with the bonus point score and captain Ben Reilly completed the rout on 74 minutes.
Garryowen's fifth defeat in six games leaves them eighth, just four points off the bottom of the table.
Meanwhile, promising out-half Matthew Gilsenan contributed 12 points off the tee as UCD gained a 32-16 bonus-point victory away to St Mary's. Gilsenan got one over older brother Conor who came on as a replacement for Mary's, while Peadar Timmins and Nick McCarthy both crossed the whitewash for the students.
The basement battle at Lakelands, meanwhile, went the way of Terenure College as they outscored Old Belvedere by three tries to two in a 24-20 win.
This was a gripping contest, Terenure full-back Jake Swaine converting his own 78th-minute try to secure four hard-earned points in their bid to avoid relegation from Division 1A.
Terenure have pushed three points clear of Belvedere and now have just a point to make up on eighth-placed Garryowen.
Bryan Mollen's 77th-minute penalty guided Dublin University to a famous 15-12 success against play-off chasing Young Munster in Greenfields.
Left winger Mollen was kicking in the absence of regular out-half Jack McDermott and emerged as the students' late hero.
Trinity stormed out of the blocks, with tries inside the first 23 minutes from forwards Tom Ryan and Pierce Dargan, with Mollen landing the first conversion.
The depleted home side steadied themselves with a converted effort from young flanker Dan Walsh just before the interval, and the second half was just three minutes old when Cookies replacement Elie Mundu raced away to touch down out wide.
The sides were cancelling each other out until Munsters were penalised for not releasing and Mollen stepped up to fire over the match-winning kick three minutes from the end.
The result has sent Trinity up to sixth place and away from relegation trouble. Meanwhile, at the business end of the table, Munsters have dropped from second to fourth but they have a nine-point advantage on UCD in fifth.
Sunday Indo Sport