United went seven points clear on top of the table courtesy of a 2-1 win, thanks to Wayne Rooney's double, but Ferguson admits he was happy to come away with maximum points after the Saints pressed them in the second half.
"That's (a win) is the only thing we can take out from it. Second-half Southampton played probably the best any team has played here this season. I thought they were very, very good," said Ferguson.
"For half an hour we were absolutely fantastic - it could have been five. We hit the post twice, Robin (van Persie)'s missed a chance, Danny Welbeck's missed a chance, we were really fabulous.
"But second-half when the pitch started to dry out, we found it very, very difficult and we're just glad we won the game."