Niall Quinn's disastrous start to his managerial career reached crisis point as defeat by newly-promoted Southend sent Sunderland bottom.
Adam Barrett headed the Shrimpers in front on the stroke of half-time and then stooped to make it 2-0 after the hosts failed to deal with a free-kick.
Lee Bradbury sealed a fine win when he tucked away Mark Gower's low cross.
Jon Stead grabbed a consolation but it failed to lift Sunderland, who are without a point in four games.
Southend boss Steve Tilson:
"I'm pleased to get another win. Also, Freddy Eastwood didn't score and we've still come up with three goals so that's pleasing.
"It doesn't matter if you're Sunderland or Colchester or Southend, it's tough when you are losing games to get out of a bad run."
Sunderland manager Niall Quinn:
"There's a percentage of players in the dressing room who are simply not good enough.
"We've put our arm round them and looked after them over the past few weeks but the losing mentality is rampant in this dressing room.
"When you see that you realise some just aren't going to make the cut."
Southend: Flahavan, Francis, Prior (Peter 38), Barrett, Hammell, Campbell-Ryce (Lawson 73), Guttridge, Maher, Gower, Bradbury, Eastwood (Hunt 84).
Subs Not Used: Cole, Collis.
Goals: Barrett 45, 68, Bradbury 89.
Sunderland: Alnwick, Wright, Neill Collins, Cunningham, Robbie Elliott, Stephen Elliott, Leadbitter (Riera 55), Whitehead, Delap (Kyle 70), Stead, Murphy.
Subs Not Used: Lawrence, Ward, Danny Collins.
Booked: Whitehead, Wright.
Goals: Stead 90.
Ref: J Singh (Middlesex).