The Saints have sustained a push for the top-four throughout the campaign and Tadic thinks that their good form has caused opposition teams to start raising their game against them.
A win over Southampton is now considered a notable scalp and Tadic feels that teams have started to put in more effort against them as a result.
“Everyone now when they play against Southampton, they give more energy, but this is normal, it happens during the season – you go up and you go down and these are normal things," he said.
The increasing standard of opposition teams may be partly to blame for Southampton's poor form of late.
The Saints have had their Champions League bid dented by a run of disappointing results, but they did get back to winning ways last night.
Ronald Koeman's side picked up a vital 1-0 win over Crystal Palace yesterday evening, with Sadio Mane's late strike providing them with the three points.
It means that they have set up a hugely exciting end to the campaign, with Koeman targeting five more wins to ensure they make it into Europe next season.