The Irish giants, as they did in 2013 and 2016, claimed a huge success in Northampton, scoring seven tries as they won 43-16.
It means they have taken charge of Champions Cup Pool 1 ahead of next Saturday's return game at the Aviva Stadium in Dublin.
And Saints were left to rue a difficult second half, in which they were unable to score a single point.
"We competed fairly gallantly in the first 40 minutes," said Boyd, who had seen his side take a 16-14 lead before Leinster went in 19-16 up at the break.
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"We said in the shed at half-time that a fair amount of juice had been taken out of the legs but we were still in the game.
"We had a period of 15, 20 minutes where we had a lot of possession and territory but came away with zero - I thought they defended really well.
"We didn't ask enough questions, we weren't patient enough and we didn't execute our skills well enough but they were very good defensively.
"Then we conceded three tries at the end when there wasn't a lot of petrol in the tank, which was the disappointing part really.
"They're one of two or three teams in Europe who can take the intensity up to somewhere near Test match level.
"It's something we don't have to cope with very often in the Premiership and that's why the Leinsters of this world have been successful or close to successful in Europe over the years.
"When they need to go up a gear in that physical intensity part of the game, they've got some answers.
"If you look at the way the big Irish teams are able to manage their squads, it's very different because the Premiership asks questions of teams every week.
"If you look at how often their big players play and are kept fresh, it is a good advantage for them.
"But you've got to deal with what you've got to deal with and we had some chances that we didn't take, which was disappointing.
"I don't know how many times we got five or six metres from their line and didn't get across.
"It's part of our education, isn't it?"