The Shrimpers could yet claim the third automatic spot in League Two if they win next Saturday and Torquay and Crawley don't.
First-half goals by Ryan Hall and Bilel Mohsni put Southend in complete control, and they had little trouble in defending their two-goal lead against an out-of-form Oxford side, who have slipped out of the play-off positions after a six-game winless run.
Sturrock said: "The fat lady still isn't singing yet, so we go into the final game of the season with still everything to play for.
"I was delighted with the performance, the workrate and the attitude of the players. It was always going to be backs to the wall in the second half.
"We knew that, but we defended well and it's another clean sheet, which I'm delighted with."