St Mirren are leading Dundee United 2-0 at the half-time interval at Tannadice.
Paul McGowan gave the visitors the lead after 22 minutes when he headed home Marc McAusland's cross.
Steven Thompson came close to making it 2-0 via the same route, but his header went just wide after 35 minutes.
However, Thompson made no mistake when his next chance arrived five minutes later as he converted from close range following a corner.