Saints fired eight goals past Sunderland on Saturday.
"Of course we can be very satisfied with the result," Alderweireld told the Daily Echo.
"The second half was much better than the first but we have to keep calm. It is only three points and next week will be tough.
"We can be happy but from tomorrow we have to be focused on Saturday because it is a big day again. It can change very quickly in the Premier League."
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