Leinster Rugby moved back to the head of Conference A of the Guinness PRO14 with a seven-try win at Parc y Scarlets.

They earned a four-point lead over Ulster with the provinces due to meet in Belfast on March 6.

Initially, Scarlets gave an early glimpse of potential in attack when Jack Conan’s carry from the restart was recycled, only to pop loose for prop Javan Sebastian to pounce and No 8 Uzair Cassiem to whip the ball away to set up an attack which allowed Sam Costelow to strike the opening points from a penalty.

Harry Byrne’s high restart and Cian Kelleher’s contest in the air forced the first competitive scrum for Tadhg Furlong after a spell on the sidelines and the tighthead had an immediate impact on Phil Price.

Another steepling restart from Byrne yielded a Leinster scrum and subsequent free-kick, Conan taking off from his own 22 for captain Luke McGrath to kick for position.

Dane Blacker’s clearance on the full gave Leinster a lineout which they quickly turned into a gain of yards, Byrne putting Kelleher in space before Dave Kearney’s pass went forward off Max O’Reilly, making his second start at full-back.

O’Reilly was soon back in the action, launching a kick that Ciarán Frawley gathered, the latter’s second touch allowing Byrne to spin a flat ball that was just beyond the fingertips of James Tracy.

Kelleher was alert in shutting down Johnny McNicholl when Blade Thomson’s skill opened the door for Scarlets to make inroads. Ryan Baird and Liam Turner emphatically sent Thompson backwards in the tackle.

Leinster went more direct from their next lineout, the maul moving to generate the momentum for runners to stream through, Byrne’s kick and Kelleher’s chase forcing a penalty.

When Conan was stopped short by Blacker and Costelow from a five-metre scrum, Dan Leavy was on the premises to ground out the try.

Scarlets bounced back in style when Costelow found Cassiem cutting a sharp angle to beat the first line of defence. Blacker was supporting on the inside for the touchdown, Costelow’s conversion nudging the home side back in front.

Once again, the chase of Kelleher was exemplary, nailing Ryan Conbeer, to force Blacker to find touch.

Tracy and Conan connected at the lineout. Frawley almost released Turner with a sizzling pass and a penalty came from a tip-tackle on Byrne.

Leinster decided on going to the corner. Baird rose highest for Tracy’s throw and the maul developed quickly. Tracy was there to claim the second try.

A period of kick-ball concluded with Scarlets blinking first, losing their discipline to hand Leinster a comfortable gain through Byrne’s penalty kick-to-touch.

Leinster’s lineout functioned well again to spark an attack in which prop Price gave away his second penalty in as many minutes, Byrne chipping the penalty accurately for 17-10 on the half-hour mark.

The visitors weren’t as long as they would have liked in clearing their lines.

A swift attack, spearheaded by centre Steff Hughes, was stopped by McGrath’s takedown, Scarlets coming back for Costelow to kick three points for a high tackle.

In a theme of the evening, Byrne’s superb restart was recovered by Leavy to set another attack in motion. Sam Lousi was penalised. Leinster went for the lineout. Tracy targeted Ross Molony to the front.

The penalty try came when Cassiem arrowed into the side of the maul and the No 8 was also binned for good measure.

Not content, Leinster came calling as the clock turned red. The lineout was good enough again. McGrath broke on the short side to slip Kelleher inside Costelow and Conbeer for the bonus-point. Byrne’s conversion made it 13-31 at the interval.

Leinster were quickly back down to business, moving the ball sweetly and with O’Reilly delivering a monster touch from inside his 22.

Then, Scarlets carved out an attack through subtle offloading to require Leavy to sweep across in defence on Tyler Morgan. McGrath was well-positioned to deal with danger on the right.

Jamie Osborne was introduced for his first cap and immediately drove McNicholl back a whopping 10 metres with a little help from Kearney.

Then, Osborne was featured in Leinster’s next move, slipping a sympathetic ball to Frawley for Kearney to test Tom Prydie with a grubber.

The sky blue shirts came alive, Byrne whistling a bullet-pass for Osborne to take a sweet angle and the recycles were happening quickly.

A scrum in the shadow of the posts was the perfect position to engineer the next breakthrough, McGrath diving over for Byrne to convert in the 55th minute.

Shortly after, Conan was off the back of a scrum in a flash and Josh Murphy was on hand to threaten out wide before a left-foot kick from Byrne bounced towards the corner flag.

Scarlets were tempted to play from deep and Leinster relished the challenge to clamp down in close and out wide.

McGrath and Byrne almost worked the oracle for Kearney down the left. O’Reilly skipped around a defender outside the 40 and replacement Jack Dunne was quickly into the game.

But, when Leinster’s attack misfired, Prydie picked up the pieces and Scarlets looked for life on the far side of the field. The pace of Morgan shredded the defence and Will Homer was at his shoulder to complete a stunning counter from deep.

Wing Kelleher intercepted another Scarlets breakout on the right touchline to trigger an attack, full-back O’Reilly side-stepping Angus O’Brien for another try.

Once Leinster had repelled the predictable rebound from Scarlets, they went through the gears in another sweeping attack, Osborne doing well once again and replacement David Hawkshaw scooting in for his first try on his fifth appearance for another seven points.

Scarlets notched a consolation when O’Brien wriggled out of a tackle to accelerate to the line for the closing score of the night.