With their fate sealed and the pressure off, the home team started with a real freedom and went close when Makenzie Kirk's flicked effort went over, before Dundee defender Clark Robertson deflected a Taylor Steven cross over his own bar.
The visitors did settle into things, though. Cameron in particular began to exert a real influence, curling a long-range shot just wide.
But he wasn't to be denied on 27 minutes as he netted his 13th goal of the season, much to the delight of the large travelling support.
Like in the first half, St Johnstone made a decent start to the second, with Kirk firing an angled shot into the side netting shortly after the interval.
But also like the first half their early promise fizzled out.
Dundee thought they had doubled their advantage when Scott Tiffoney slotted the ball under goalkeeper Ross Sinclair and into the net, but his effort was correctly ruled out for offside.
St Johnstone were rarely seen as an attacking force as the half wore on, but an Adama Sidibeh shot that went just wide served as a reminder to Dundee that there was still work to do.
The away fans were cheering late on as news of County's 1-1 draw with Motherwell filtered through, a scoreline that further eased any flickering fears they may have had that their team could yet end up in a relegation play-off with Livingston.
And the three points were sealed when Cameron converted from the spot after Graham Carey had fouled Ziyad Larkeche.