Hearts' defeat at Kilmarnock on Saturday livened up the title race, as did reigning champions Celtic's win at home to Motherwell.
All three results meant Hearts ended the weekend just two points clear of second-placed Celtic, who in turn are a point ahead of arch Glasgow rivals Rangers, with eight games each remaining for the trio.
In windswept conditions at St Mirren Park, it was Danny Rohl's visitors who broke the deadlock just after the half-hour mark when left-back Rommens scored his first Gers goal since signing from Belgian side Westerlo in January with a close-range finish.
Rangers, however, were unable to add to their lead, but a lack of threat at the other end helped calm any nerves among the travelling support in Paisley.
The Buddies, who lost boss Stephen Robinson to fellow Premiership side Aberdeen during the week, barely troubled Light Blues goalkeeper Jack Butland, and they ended the day still in 10th place, above Kilmarnock on goal difference.