Nuno says his men lost control during the first period but has urged them to stick together having gone three games without a win in the league.
A slow start on enemy territory cost Tottenham Hotspur dearly as the search for a first league win after the international break continues.
The hosts were home and dry at halftime thanks to goals from Emile Smith Rowe, Pierre-Emerick Aubameyang and Bukayo Saka.
Nuno’s men fairly improved after the break and got a consolation goal from South Korea superstar Heung-Min Son during the dying embers of the game and that was not enough to conjure any magic.
"We lost complete control in the first half. We got smashed and then had a good reaction,” the Portuguese coach said.
"It's frustrating and very disappointing. It's the moment to stick together and carry on. The players were ready but we lost a bit of control. We lost the balance in the middle of the pitch.
"When you concede three goals in each of the last three league games you cannot hide the problems. But we are professional. There is a long way to go. We need to stay calm."
Spurs will lick their wounds and focus on their next two games which is against Mura and Aston Villa in the UEFA Europa Conference League and Premier League respectively.
