Mallinder has been heavily tipped to take over as Red Rose boss after the departure of RBS 6 Nations-winning boss Johnson this week but it was all about the Welsh outfit and Rhys Priestland at Franklin's Gardens.
The Wales No. 10's 13 points came from a try and the conversions from his, and three other scores courtesy of Liam Williams, Aaron Shingler and Matt Gilbert.
Last year's beaten finalists rallied late on with scores from Tom Wood and George Pisi but it was not enough to stop Scarlets claiming their second victory and top spot in Pool One.
Northampton's second successive European defeat leaves them on the brink of elimination, but it was Mallinder's international future that was highest on the agenda after the game.
"Everybody strives to be the best they can and coaching the national side is a massive honour," said Mallinder.
"I have said previously that it is (a role that interests me).
"There have been no questions asked and at this moment I am very happy and I think I have got a really important job to do, getting this side (Northampton) back up and winning rugby matches."
While the welsh region's victory at Northampton was a famous one it was edged out in the performance of the night award by Edinburgh - who turned a 24-point second-half deficit into a 48-47 win over Racing Metro 92.
Greg Laidlaw was the Edinburgh hero, with 23 points while Tim Visser's pair of tries, including the all-important late score helped settle a breathtaking clash.
And on a memorable Friday night of European action Cardiff Blues also made it two wins on the spin by beating London Irish 24-18.
Rhys Thomas and Lloyd Williams were the try scorers for the Cardiff outfit in a game which hinged on a red card for Exiles centre Steven Shingler after just 20 minutes.
Four penalties and a conversion from Dan Parks were the Blues' other points while Tom Homer's six penalties kept Irish in touch.