The Magpies succumbed to a 3-0 defeat at the hands of Paolo Di Canio's Black Cats at St James' Park yesterday.
"It's the worst day for the club, for the players, for the fans and for everyone," Tiote told the Shields Gazette.
"I'm playing for Newcastle, and to lose to Chelsea or Man United is disappointing, but not like losing to Sunderland.
"We're never happy to lose any game, especially against Sunderland. It's the worst thing for everybody at the club."
The result has placed Newcastle five points away from relegation in the Premier League.