Sunderland's former Derby goalkeeper Mart Poom scored a sensational injury time equaliser to earn the visitors a share of the spoils at Pride Park.
Poom celebrates his remarkable late leveller
Rams skipper Ian Taylor had netted in the 90th minute to seemingly secure victory for the Rams.
But Poom, who had joined Sunderland for £3m at the start of the year, produced Peter Schmeichel-style heroics to convert Sean Thornton's injury-time corner with a towering backpost header.
It had been the visitors who made the early running, with Kevin Kyle posing the first threat of the game in only the second minute, his diving header just clearing the crossbar.
But central defender Gary Caldwell, on loan from Newcastle, went close with an aerial effort at the other end after 10 minutes.
Soon the Rams were on the offensive again, a sweeping move almost paying dividends on the quarter-hour mark when Tom Huddlestone saw his powerful low drive deflected wide by Williams.
But Marcus Stewart missed a guilt-edged chance in the 21st minute with an insipid header when just inches out.
Sunderland should have reached the break in front but Thomas Butler ballooned his effort high over the bar when the goal was at his mercy.
Hostilities were resumed in earnest when, in the 52nd minute Ian Taylor wrapping his left foot around a low drive which scuttled marginally wide of Poom's woodwork.
John Oster's direct dribble cut through the heart of the Derby defence only for the ball to be run out of play before Stewart tested Oakes with an overhead effort in the 55th minute.
As the game stretched even further in its closing stages, the Rams increased their tempo and appeared to have secured their third successive victory when Taylor flung his right boot at a Valakari corner.
But in an amazing finish, Poom's thunderous header found the back of the net with seconds remaining.
Derby: Oakes, Jackson, Mills, Caldwell, Boertien, Morris, Taylor, Huddlestone, Holmes, Junior, Svensson. Subs: Grant, Zavagno, Elliott, Valakari, Labarthe.
Sunderland: Poom, Williams, Bjorklund, McCartney, Arca, Oster, Thirlwell, Healy, Butler, Kyle, Stewart. Subs: Ingham, Clark, Proctor, Thornton, James.
Referee: P Walton (Northamptonshire).