A Wallace cross caused problems inside the Falkirk penalty area, before Philip Roberts fired wide from a good position.
McCulloch headed home from a corner for Rangers and minutes later Jon Daly saw his looping header claimed easily by McGovern.
Then just past the half-hour mark Wallace went close for the Glasgow giants when he shot on goal, but McGovern made a very good save.
However, McCulloch saw his spot kick saved by McGovern and Law's subsequent goal from the rebound was chalked off because of offside.
Fraser Aird was unlucky to be denied a goal by the frame of the Falkirk goal when his shot came back off the crossbar.
However, there was no denying Law in the 89th minute of the contest when he shot home through a host of bodies after latching on to a knock-down from Bilel Mohsni.