The defeat for Ulster marked their first of the season, but even more importantly, it opened the door for Leinster – who have two games in hand – to stake a claim for the top spot in the conference for a final berth.
Leinster fought back strongly in Dublin after trailing at halftime, to eventually control the game en route to the 12-point victory.
Ulster were still in the game, on the scoreboard at least, going into the final minutes, but their hopes of a win were erased when the home side scored their fourth try.
The teams will meet again in Belfast before the pool stage of the competition concludes, and if Ulster return to their winning ways in the next few weeks they could still find themselves playing for top spot in the Conference. However, the log points they surrendered this past weekend will make it harder for them to stay on top.
The top two teams in the competition will advance straight to the final in this season’s abbreviated Guinness PRO14 season.
In Conference B, meanwhile, front-runners, Munster - who defeated Connacht 16-10 this past weekend - are in pole position for a final berth, and since they too will cross paths with Leinster, coach Johan van Graan’s men could play a role in determining who they could possible face in the grand finale.
Munster started their game against the trailing Connacht with an eight-point lead on the log and they stretched that to 11 points with the win, and their No 1 position was strengthened by the third-placed Scarlets going down 29-20 against the Cardiff Blues.
Munster’s Chris Farrell scored the only try in the first half, and with the two flyhalves trading penalty goals, the hosts took a 10-3 lead to the break.
JJ Hanrahan kicked two further penalty goals after halftime to put Munster 16-3 ahead, but that comfort was ruined by a late Connacht try, which forced Munster to hold on in the dying minutes.
Guinness PRO14 results:
Leinster 24-12 Ulster - RDS Arena, Dublin
Zebre 22-18 Benetton - Stadio Sergio Lanfranchi, Parma
Dragons 20-28 Ospreys - Rodney Parade, Newport
Connacht 10-16 Munster - The Sportsground, Galway
Cardiff Blues 29-20 Scarlets - Cardiff City Stadium, Cardiff