The defender has also moved to ease fears regarding his fitness after exiting the Bournemouth game at half time.
The Saints were 2-0 winners against Bournemouth at the weekend, but were lucky to come away with the win as they spent most of the second half on the back foot.
Fans would have been uncomfortable with the way things were going, given that they had surrendered a two-goal half-time lead to Leicester City in their previous home game.
And Fonte has urged them to keep up the intensity for 90 minutes.
“We need to do better in this kind of situations, because it’s not the first now, because again against Leicester as well we lacked a little bit of intensity in the second-half,” he told saintsfc.co.uk.
“It was a good win, but a win we need to take the positives, but also analyse this second-half performance, which wasn’t the best. It’s just a question of being ruthless and that’s it. Just never take the foot off the accelerator.”
The defender has also moved to ease any fears regarding his fitness following the game.
Fonte was forced off at half-time with a hamstring issue, with fans sure to be concerned that they could lose their key defender for a significant period of time.
He, though, says that he made the decision not to take any risks by continuing in the game, with him keen to help Ronald Koeman’s side continue their recent fine run of form.
“I’ve had two dead legs in the last couple of weeks and after the Liverpool game, I was feeling a little bit stiff,” he added.
“I made the decision that there’s no point in risking pulling something, because the league is long and we have many games, so I took the decision of coming off and not risking a bad injury.”