Sissoko, a £2 million capture from Toulouse, set up the opening goal for Papiss Cisse and impressed in his central midfield role.
Pardew said: "When you are looking for players and trying to find the secret ingredient for your team, it's not always easy for players to come and fit in as they did in the first half.
"I was a little bit surprised myself if I'm honest. I don't think we would have won the game without Sissoko. That's how important I think that signing was.
"Sissoko really grabbed the game by the horns and that's what we needed.
"With Demba Ba departing from a team that hasn't been winning, it was a big blow for us and we really needed him for this game."