France Under-21 striker Riviere claimed a brace for his first Newcastle goals as the visitors edged past Palace thanks to Paul Dummett's extra-time header.
Alan Pardew: "Anyone who has seen us play this year will know the top of the pitch has been an issue for us.
"We've just not had that cutting edge.
"So perhaps the two goals on Saturday and two tonight is a big lift for the club.
"I'm so pleased for Manu, he's worked tirelessly this season, and he deserves those goals.
"That will give him a real lift.
"Paul Dummitt is a local lad and he's having to prove to the Newcastle public that he's good enough, it's hard for players to come through the academy these days.
"Sadio gets a bit more glamour than Paul, but Paul does what it says on the tin.
"He's a tough tackler, good in the air, getting better going forward.
"How he's ended up in the middle of the goal at that time, I don't know."