A goalless draw at Arsenal on Wednesday evening secured the Black Cats’ top-flight status with a game to spare.
The result left Advocaat, who took over with nine games of the season remaining, in tears at the final whistle as his side celebrated avoiding the drop.
“It’s unbelievably important for the club that we stay up,” he told Sky Sports. “We’ve come far. If you look at the last six games, the team is working unbelievably in training but also in the games.
“We still knew that we had a chance on Sunday and that Newcastle had to win and Hull had to win. But this gives us an unbelievable feeling that we did it by ourselves and that’s the reason why everybody now has to be very, very happy.”
Advocaat was appointed on a deal until the end of the season and says he will make a decision on his future next week, after admitting the club is growing on him.
“Definitely,” he said. “Because the players gave everything for the club. For themselves but also for the club and the fans. It’s a beautiful stadium we have and the training facilities are great but the last couple of years, we were not always lucky.”
Asked about his future, he said: “I don’t know. We stayed up and that’s the most important thing. I’ll decide next week.”
Since taking over at the Stadium of Light, Advocaat has lost just twice, and the draw at Arsenal made it five matches unbeaten in a row.
“The most important thing is that they started believing that they could do something,” he commented.
“I always said that you are not at this club because you are a nice guy, you are here because you are a good player. If you keep saying that and keep them practising and training, giving them the goals which is what you need, then even against the better teams you can get the results.”