The Dons showed their clinical side as they punished the home side on the counter-attack and three points takes them alongside Celtic and Hibernian..
Johnny Hayes fired a low shot beyond Craig Samson to open the scoring after 10 minutes and the in-form Niall McGinn doubled the visitors' lead on the stroke of half-time, ending a lightning-fast counter by slamming the ball high into the net.
Chris Clark drilled a low shot past Samson with four minutes remaining to put the game beyond Saints before late strikes from Mark Reynolds and Steven Thompson rounded out the scoring.
A fabulous second half from Kilmarnock saw them claim a comfortable 3-0 home win over Ross County.
Two goals from Paul Heffernan, making his first start of the season after recovering from a dislocated shoulder, and a superb strike from Gary Harkins had the Rugby Park fans celebrating after two home defeats.
Dundee provided further evidence that they could mount a serious fight against relegation as Nicky Riley's strike earned them a 1-1 draw against Motherwell.
Riley struck against the run of play before Motherwell finally made their first-half dominance count in injury-time when Michael Higdon followed up after Rab Douglas had stopped Henrik Ojamaa's shot.