Lloyd Jones struck Charlton’s seventh-minute opener after West Ham allowed a long throw-in to bounce inside their penalty area and Tyreece Campbell put Charlton 2-0 ahead when Konstantinos Mavropanos was dispossessed near his own penalty area after the break.
“We created a lot of situations but we weren’t accurate enough in the boxes,” said former Wolves and Nottingham Forest boss Nuno, speaking after his team had more than 77% of possession and finished on an expected goals total of 2.96 to Charlton’s 0.57.
“We have to defend much better. We had a lot of possession and tried to break them down, which is not easy.
“We were still able to create a lot of situations that we should – and will, for sure in the future – finish better.”
He continued: “This season, it’s clear that we’re going to be protagonists and will have more of the ball.
“We [will work on] combinations in the final third and in one-on-ones, creating situations that can allow us to score.
“We’re going to repeat, repeat, repeat – but keep the belief in the process. We’re going to get together and bounce back.”
West Ham’s next match is a Carabao Cup tie against Southampton on Tuesday, with league matches against unbeaten duo Watford and Wolves to follow.