Ospreys captain Alun Wyn Jones says George North has "improved as a player" since joining Northampton.
The 22-year-old Wales wing scored four tries as Saints crushed Ospreys 34-6 in a Pool Five Champions Cup match.
North joined Northampton from Scarlets in the summer of 2013.
"I think since he's been up here he's improved as a player a great deal and, like Northampton as a side, he was ruthless and when he got a sniff he took the opportunity," said Jones.
"I suppose it's a positive we can take out of it it was a Welshman that scored all the tries."
Jones and North are both in the Wales squad which meets on Monday for the four-match autumn Test series.
Wales face Australia on 8 November, followed on consecutive weekends by Fiji, New Zealand and South Africa.
Ospreys were unbeaten going in to the match at Franklin's Gardens for a match which pitched the top clubs in the Aviva Premiership and Pro 12 against each other.
The Welsh region's run included a win over Munster in Limerick and Welsh derby wins over Dragons and Blues.
But Jones conceded that Northampton were the better side, though conceded North's fourth try minutes from the end - which earned his team a bonus point - was a blow.
"I thought they were ruthless as we expected them to be," he said.
"The late try was arguably one of the most disheartening because - without being defeatist - it was damage limitation at that stage.
"We wanted to make them get the four points not the five and he's [George North] kept working on his own there, got the ball and run it in.
"In fairness to the boys have tried to cover, but when he's in that sort of form it's difficult.
"We went into [the game] with confidence after what we've done in the Pro12.
"We're not saying we're brilliant - we know we're not brilliant - and you can only beat what's in front of you and we've done that to a degree where we're still not happy with it.
"We knew a stern test was going to come along. We had to punch above our weight, which we've done already, but we didn't do that."
Ospreys' next matches in the Champions Cup are against Racing Metro on 6 December and 13 December.