Pat Lam's men arrived in Dublin full of confidence after two successful weeks in the European Rugby Champions Cup, beating Toulouse and Zebre, but Leo Cullen's side cut them down in the Irish capital and moved top of the Guinness PRO12 table.
Adam Byrne and debutant Barry Daly both scored tries for the hosts, but it was captain Isa Nacewa's 14 points from the tee that proved decisive, while Leavy, Sean O'Brien and Jack Conan put in a fine performance in the back-row as Leinster extended their home winning streak to 19 matches.
Man of the Match Leavy, 22, was particularly pleased that they denied a bonus point to the ide that humbled them in May.
"The fact they took a title off us last May added spice to it, gassed the flames to it and a lot of the guys are beaten and bruised," Leavy explained.
"These are good times and it was a great win against a quality side. We denied them a bonus point too.
"This was an interprovincial game, there is always bragging rights and you always want to beat your neighbours."
Gianluca Guidi hailed his Zebre side's courage after they turned over Edinburgh 19-14 in the Scottish Capital.
Zebre and Edinburgh went into Friday's game at BT Murrayfield at opposite ends of the spectrum - Guidi's side short on confidence after a chastening couple of weeks in Europe, while Edinburgh were buoyed by three-straight wins and a thrilling 36-35 Challenge Cup win over Harlequins.
The Italians had shipped 134 points in their previous two European games, but after surging into a 12-0 lead, they scored late on for a famous win.
Ross Ford and Murray McCallum tries looked to have rescued victory for Duncan Hodge's side, but Giovanbattista Venditti crossed at the death.
Guidi was both relieved and delighted after his side showed phenomenal resilience to recover from their European struggles.
"This victory belongs to the players: they were great. It wasn't easy to produce a great performance after a negative break during the Champions Cup, it's a win for the entire squad," Guidi said.
"It's a squad of courageous boys and men who have shown a bond to the team and friendship among themselves.
"I want to especially thank my wife and my two children: during a difficult period they have been my strength.
"This evening we showed that we are a strong squad and that nothing can hurt us."
It took both Scarlets and Rhys Patchell a while to settle down this season, but after a fourth-straight Guinness PRO12 win on the No. 10's return to BT Sport Cardiff Arms Park, things are looking up for Wayne Pivac's side.
Aaron Shingler, Steff Evans, Hadleigh Parks and DTH Van der Merwe all crossed, with Patchell kicking three conversions in a 26-15 win.
And Patchell, who spent five years with Cardiff Blues, acknowledged that the Scarlets were starting to hit their straps.
"It's pleasing but it's not so much about me coming out on the right side of the result, it's a lot more about us coming out on the right side of the result. It was a big night for us, we needed to win," the 23-year-old said.
"It's pleasing, at the end of the day the boys put in an incredible 80 minute shift."
Munster picked up where they left off against Glasgow Warriors in Europe, powering to an impressive 15-14 win at the Kingspan Stadium on Friday.
Charles Piutau scored his first Ulster try, but Munsterman Rory Scannell was the star of the show as his try and late drop goal helped Rassie Erasmus' side to a crucial win that moved them fourth in the league table.
Warriors rebounded from their European loss at Thomond Park with a bonus-point win over Benetton Treviso at Scotstoun - Rory Hughes grabbing two tries.
And Keelan Giles continued his superb start to life on the Ospreys wing, scoring two more tries - making it eight in his first four regional games - as Steve Tandy's side kept pace at the Guinness PRO12 summit with a 35-17 win over Newport Gwent Dragons.