Rowan Vine scored the only goal at McDiarmid Park when he drove home from close range after Murray Davidson had bundled the ball towards the line when Mehdi Abeid's corner bounced in the six-yard box.
The Perth side followed their draw with Celtic - the first of three consecutive midweek games - by building on their 52nd-minute lead with Gregory Tade, twice, and Frazer Wright heading against the frame of the goal in a comfortable second-half display.
The goal followed a scrappy first half on a bumpy surface but Lomas was not concerned with aesthetics.
"The aim was to get the three points, I didn't care how we got them, by hook or by crook," he said.
"We had a tough game away at Ross County on a heavy pitch and then a tough game against Celtic on Wednesday. That was three tough games in a week and we knew this wouldn't be one for the purists.
"The first goal was critical and we got it. St Mirren had to come out and expose themselves a bit more.
"They opened up a little bit and it allowed us to hit them on the counter-attack.
"It could have been a bit easier but for a couple off the woodwork.
"All credit to the boys, we have had this ridiculous situation with six games in 23 days and then three weeks off."
- Sports & Recreation
- Mehdi Abeid
- Murray Davidson
- Gregory Tade