With many of Leinster's troops still away at the Rugby World Cup, Barclay senses an opportunity to make it four from four.
And the flanker, who committed his future at Scarlets until at least 2017, has urged his side to not let their fine start slip.
"In terms of our season so far I don't think we've played particularly well yet," he said. "We've played well in patches and defended well but we still have a lot of work on.
"It was certainly a great start. To knock off Glasgow and Ulster was huge but there are a lot of aspects of our game that need fine-tuning.
"It's nice to now have three in a row to try and keep the momentum going and get more fans down here watching and give the new guys a cheer at home.
"Leinster will undoubtedly be a difficult opposition despite missing their international contingent. They have some wise heads steering the ship.
"They're always a gritty team to play against and they'll no doubt be disappointed with how their season went last year and looking to put that right."
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