The Hornets have propelled themselves into 11th place on Premier League on 30 points. But they're still only six points above the drop zone.
Janmaat, who scored on Monday night, spoke to Sky Sports about how the club must build on the unexpected victory.
He said: "I know I can score goals, I did it in the past last year against Chelsea as well.
"It is really good, I am happy for the team and it is a really important win. We pressed them well. We won a lot of second balls.
"Last week in Stoke we had a good result, a point there, and three points today. We have to build on from here because we want to be safe as soon as possible."