The win allowed Saints to leapfrog their hosts into fourth spot in the SPL table, with Rowan Vine netting a brace before the break, with Patrick Cregg adding a third on 58.
Leigh Griffiths pulled a goal back nine minutes from time but by then it was too little, too late for the Edinburgh side.
And manager Lomas said: "We really enjoyed our European adventure (last summer in Europa League qualifying) and we would love to get back there but it's so tight this year and we've got a lot of tough games.
"But I did say to the lads that we've got eight games and that's our cup run.
"What can we do? Treat each game as a cup final and see where it takes us."
As for the victory, he added: "It was very good from start to finish.
"We've had a few games this season where we have had good performances and sometimes haven't got what we deserved.
"But I thought we thoroughly deserved this win and if it had been by two or three more, there probably couldn't have been much complaint."