Southend secured the League One championship thanks to Wayne Gray's 87th-minute winner.
Gray came off the bench to grab the winner just three minutes from time as the match appeared to be heading for a drab goalless draw.
Gray latched onto Kevin Maher's pass to seal the title with a powerful deflected shot.
City were the better side before the break, with their best effort coming from David Noble's long-range drive.
Southend: Flahavan, Jupp, Hunt, Barrett, Wilson, Bradbury, Guttridge (Bentley 80), Maher, Gower (Cole 69), Eastwood, Goater (Gray 83).
Subs Not Used: Pettefer, Lawson.
Goals: Gray 87.
Bristol City: Basso (Abbey 65), Orr, Carey, Keogh, Woodman, Cotterill, Noble, Skuse, Wilkshire (Brown 75), Brooker, McCammon (Williams 61).
Subs Not Used: Savage, Wilson.
Southend are champions
Ref: K Stroud (Hampshire)