"I didn't know what was going to happen but in our heads we knew that the victory was imperative," Sissoko told the club's official website. "We had to go out there and fight and keep belief within ourselves.
"This is our spirit - we've got a great team spirit and we knew we had to go out there and win.
"We got the goal in stoppage time which just shows how fantastic the mentality is here, to go out there and fight until the very death and make sure we stay up."
Newcastle face Benfica in the second leg of their Europa League quarter-final tie before taking on rivals Sunderland next week in the Tyne-Wear derby.