Rafa Benitez had to shout at Kenedy moments before his goal-saving challenge – because he was starting to "relax".
Kenedy ran back to slide in and challenge Watford's Andre Gray during Saturday's 1-0 win at St James's Park.
The winger's intervention stopped what looked to be certain goal.
United manager Rafa Benitez had seen the danger from the quick break forward and yelled at Kenedy to get back to challenge Gray, who had come off the bench after Ayoze Perez had scored.
The 22-year-old, on a season-long loan from Chelsea, did just that and timed his tackle perfectly.
“If you see on the TV, I was shouting at him, because I knew it was very dangerous," said Benitez.
"I was shouting at him, because I did not want him to relax. Sometimes you relax and then you cannot get back, but he did very well. I could see the player and was shouting at him and telling him he had to go. He did well."
The result, the club's first win of the season, lifted Newcastle out of the Premier League's relegation zone.