Dan Jones and Steve Shingler eventually booted a dogged Zebre - who were leading 8-6 at half-time - out of contention at Stadio Sergio Lanfranchi, and fired Scarlets towards their record seventh PRO12 victory in a row.
The momentum switch came when flanker James Davies bundled over off the back of a rolling maul to put Wayne Pivac's men in front for the first time, leaving Jones and Shingler to do the rest.
But Scarlets are not the only side in form, John Andress and Phil Burleigh scoring a try in each half to inspire second-place Edinburgh to a 20-9 victory over an Ospreys side who are yet to win this season.
Edinburgh had won the last six clashes between the two teams and, despite a slow start, began to assert their dominance at the scrum before fly-half Burleigh crossed over.
Sam Davies' three penalties put Ospreys - GUINNESS PRO12 semi-finalists last year - up by two heading into the break, but Greig Tonks was on target with two penalties and Andress' try left the visitors with no way back.
And just behind Scarlets and Edinburgh on points difference is Munster, who went some way to avenging last season's PRO12 final loss at the hands of Glasgow Warriors by edging a tight one at Thomond Park 23-21.
The Warriors, who are missing 21 players to international duty, did not go down easily - and Rory Clegg enjoyed a brilliant night from the tee with a 21-point haul.
It had put Glasgow on the brink of victory but Ian Keatley's last-gasp penalty, that brought his kicking tally up to 13 points, proved enough for the Munstermen alongside BJ Botha and Dave O'Callaghan tries.
Elsewhere Connacht battled to a helter-skelter 36-31 triumph over Cardiff Blues and are just one point behind the chasing pack after collecting three bonus points already this year.
Inspired by man of the match Nepia Fox-Matamua - who touched down in the first half - Aly Muldowney's converted try ultimately proved the difference, though the Blues did grab a bonus point of their own at the death through Sam Hobbs.
Isa Nacewa got the RDS rocking on with a first-half try double as Leinster powered to both the 37-13 win and a bonus point over Newport Gwent Dragons.
Cathal Marsh and Garry Ringrose added two further tries for Leinster in the second half, ensuring back-to-back wins after their season-opening defeat at Edinburgh.
There are just two points separating the top six and Ulster also made sure they're in the conversation after Craig Gilroy crossed twice against Benetton Treviso on a night that saw Andrew Trimble become Ulster's most-capped player.
Gilroy was joined on the scoresheet by Lewis Stevenson, Paul Marshall, Dan Tuohy, Pete Browne and Sean Reidy, with Ulster opening up a 22-point gap by the break.
TRY OF THE WEEKEND
There were nine tries to choose from in the clash between Connacht and Cardiff Blues alone but the nod is given to Danie Poolman's effort after some superb instinctive passing in the build-up.
Starting just inside the Connacht 22, Jack Carty pulled off reverse pass into the path of Bundee Aki, who had the presence of mind to loft the ball on to his fellow centre Rory Parata before he got clobbered.
Parata's decision-making was even quicker, helping the ball on to Poolman under pressure and the sucked-in Blues bodies were helpless to prevent the South African going over in the right-hand corner.
BREAK OF THE WEEKEND
Craig Gilroy was an unlucky omission from Ireland's World Cup squad but he hasn't let it affect his form at Ulster after creating a try out of nothing against Benetton Treviso.
The winger received the ball at close to full pelt and he caught Treviso unawares, concertinaing through the Italians' line.
Such was his incisiveness that he was only touched when he was halfway over the whitewash already - having started the break from his own half.
PLAY OF THE WEEKEND
Leinster were perhaps not quite at their fluid best but they turned on the afterburners when they needed to - and there was no better exponent of that then Noel Reid.
After taking on an offload Reid was presented with a hole but still had to turn two defenders inside out before kicking a gloriously weighted chip over the top.
Isa Nacewa won the footrace with Tom Prydie and touched down for his second try of the afternoon against Newport Gwent Dragons, but it was of Reid's making. Indeed, Reid had also set up Nacewa's first with a sumptuous pass.
PLAYER OF THE WEEKEND
It's not often a player on the losing side deserves this kind of the award but for a threadbare Glasgow Warriors side, Adam Ashe nearly drove them to an unlikely victory at Thomond Park.
The No.8 was a constant menace at the breakdown and managed to outshine opposite number CJ Stander, who barely goes a week without being named man of the match for Munster.
Thanks in much part to 22-year-old Ashe's efforts, Rory Clegg - who enjoyed a stellar night of his own with a 21-point haul - nearly won it for the Warriors, but Ian Keatley had the last say.
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