Leinster started slowly against the Scarlets but finished with seven tries to keep the pressure on Ulster at the top of the United Rugby Championship table at the RDS Arena this evening.

Scarlets started brightly when their fly half Sam Costelow punished a Leinster foul to open the scoring with a penalty on the first attack just two minutes into the game.

Returning Lion, Johnny Sexton levelled matters from a penalty five minutes later when Scarlets full back Ioan Nicholas was penalised for not releasing in the tackle under pressure from the Leinster defensive line.

The Welsh side, who came into the encounter carrying a major underdog tag, looked like they hadn't read the script in the early exchanges and drew first blood when a combination of Nicholas and Johnny McNicholl found an bit of space on the Leinster wing and McNicholl powered home into the corner for the first try of the game.

Costelow was unable to add the extra two points as he pulled his conversion attempt well wide of the near post from his kicking position just along the sideline.

The score seemed to wake up the favourites as they grew into the encounter and their physical advantage started to bear fruit on the field and on the scoreboard.

A well worked lineout routine saw Ronan Kelleher benefit from the pack shove and he touched down for a try which Sexton was unable to convert.

Just before the half hour mark Leinster were ahead with Andrew Porter finding a gap with a pick and go just shy of the Red's line to increase the lead as Sexton added the extras.

Leinster passed the kick at the posts just before half time and Jamison Gibson Park nearly squeezed over in the corner but the referee awarded a penalty try to Leinster to put them fourteen points ahead at the break.

The home side opened the second half as they finished the first when a burst from hooker Ronan Kelleher broke through the Scarlets line and he fed Caolan Doris for the flanker to cross for his first try of the season.

Interestingly enough, centre Ciaran Frawley stepped up to add the conversion despite Johnny Sexton still being on the field.

Both placekickers would leave the action shortly afterwards. Frawley due to the HIA after a clash of heads with Gareth Davies after a collision while Sexton's day was completed as he was withdrawn for Ross Byrne for the last half hour of the encounter.

Scarlets showed that they had a little bit of bite with an excellently worked break which ended with Tomas Lezana touching down for substitute out half Dan Jones to convert to give the Scarlets some hope.

Frawley returned to the field after the concussion protocol was followed and his first interaction was to carry the PRO14 champions to the Welsh side's try line, eventually the experienced Cian Healy found a gap and secured his first five pointer of the season.

Ross Byrne added the conversion which effectively ended the game as a contest with almost twenty minutes left on the clock.

Scarlets try scorer Johnny McNicholl found himself in the sin bin late on and Leinster sub Dan Sheehan took advantage competing for a cross field kick he rose highest and added the final and seventh try of the game with Ross Byrne adding the conversion for a winning scoreline of 50-15.