But Mike Ross' first GUINNESS PRO12 try after the interval combined with the boot of Ian Madigan - who kicked 14 points in total - saw Leinster run out 19-15 winners.
The first loss of the campaign sees Scarlets drop to second, with Connacht moving top of the pile, but back-rower Barclay believe six wins from their first seven games constitutes a solid start as their attention now turns to European action.
"It's encouraging," said Barclay. "We have plenty to work on but we're winning our games and it's going ok.
"[Against Leinster] we saw a little bit of indiscipline and we coughed up the ball too cheaply at times.
"It's great to come here and get a bonus point but we're pretty disappointed to lose that game.
"Last year we came here and probably had the worst form of the season, it's probably one of the hardest places to come and play, they've got a great record here.
"The fact that we're disappointed is good but it's these games at the end of the season that you look back on and think 'what if', so it's a bit disappointing."
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