The St Mary's club conceded 60 goals last season - only two teams outside the bottom three fared worse - as they finished just five points clear of the relegation zone.
But manager Mauricio Pochettino has worked hard to strengthen in the close-season and Croatia international Lovren was among the new additions.
The 24-year-old has started all of the side's opening four league matches, in which they have conceded just two goals, and Fonte believes that Lovren has been a huge factor in their improvement.
"He's a great player first of all, and when you have a great player next to you it's easier to play," the Portuguese player told the Daily Echo.
"I feel confident with him, we understand each other well. It's always going to get better, because we're still getting to know each other, but from the first moment I had a good understanding with him.
"I know more or less what he’s going to do in each situation, and he knows what I'm going to do, so at the moment we're in a very good place and I hope this partnership keeps developing and improving."
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