Kyle Benedictus set Dundee on their way to a 3-1 home win to end high-flying Hibernian's tenure at the top of the SPL.
The victory lifted bottom-of-the-table Dundee to just a point behind St Mirren as Barry Smith's side continued their recent run of fine form.
Benedictus scored in the first half and his effort was followed by second-half goals from Steven Milne and Kevin McBride which meant Leigh Griffiths' injury-time strike was nothing more than a consolation.
After 20 minutes Benedictus broke the deadlock in style with a spectacular strike from 20 yards.
Jim McAlister's corner was only half-cleared by defender Lewis Stevenson and defender Benedictus turned neatly to send an unstoppable effort from his weaker left foot into the top corner past the helpless Williams.
Then, on the stroke of half-time, Davidson was unmarked just yards from goal but headed wide from McAlister's inch-perfect cross and the chance to go 2-0 in front went begging.
But after 48 minutes Dundee increased their lead. Lockwood's inswinging free-kick was headed down by defender Declan Gallagher and Milne was on hand as he reacted first to prod the ball home from point-blank range.
And after 51 minutes they killed the contest by making it 3-0. Former Hibernian hitman Colin Nish was brought down by Alan Maybury as they both chased Gallagher's through-ball.
Midfielder McBride stepped up to send the penalty past Williams who had no chance, to send Dens Park wild with delight.
Dundee attacked the visitors' goal towards the end, looking for a fourth goal, and not even Griffiths' late 25-yard strike could spoil their day.