Saints scored 10 tries on their way to a thrilling 65-26 win against the Falcons, who were playing their last game under Richards.
It was a crucial win for Saints as they booked their Gallagher Premiership play-off place, meaning they will now travel to Leicester Tigers for a semi-final showdown next Saturday.
Richards was left to rue a couple of disciplinary issues as a yellow card for Greg Peterson and a red card for Sean Robinson hampered Newcastle’s victory bid in Northampton.
"The red card didn’t help much at all – at the point, it was probably the turning point for us," Richards said.
“Having said that, I thought their nine and 10 were outstanding and when they lost their nine to a yellow card, that sort of hampered them quite a bit.
“On the day, I thought they probably were two or three scores better than us and when you’re chasing a game and you get within a few points, as we did do, sometimes you’ve got to tighten things up and we didn’t.
“We carried on playing and that loose way, even when we were down to 14 men, sometimes it can come back to haunt you a little bit.
“But full credit to the boys; I thought they stuck at it.”