Doubles from Shota Arveladze, who was playing his last home game for Alex McLeish's side, and Thomas Buffel were enough to secure the win but it could have been by a much greater margin with better finishing.
The gloss was slightly taken off their victory when for the second week running Marvin Andrews put through his own goal near the end.
The result means that the title race will not be decided until the final matches next Sunday.
Rangers pressed early on but Dado Prso's effort from Nacho Novo's cutback lacked the power to trouble Gordon Marshall.
Novo then sent over another super cross which Arveladze should have done better with than head over.
Buffel put Rangers ahead with a well-taken 12th minute goal. Latching onto Prso's header the Belgian survived a wild tackle by William Kinniburgh before steadying himself and side-footing the ball under the keeper.
Rangers increased their lead five minutes later. Marshall did well to parry Arveladze's shot from the edge of the box, but Prso latched onto the loose ball and from his cross Arveladze volleyed home.
Marshall saved well at the feet of Prso as Rangers went after more goals although the visitors threatened when Scott McDonald's cross was just missed by David Clarkson in front of goal.
Novo was always a menace on the Rangers right flank with Shaun Fagan and Marc Fitzpatrick toiling in his wake. Buffel rounded Marshall but Paul Quinn recovered in time to clear the ball off the line.
Prso lobbed over from another excellent Buffel pass before the Croatian striker was guilty of too many touches as he failed to get a shot in after beating three defenders in the Motherwell box.
The Steelmen improved after the interval and Richie Foran headed against the bar although he was adjudged to have fouled Fernando Ricksen in the process.
Clarkson then latched onto a sliced Andrews clearance but his touch was poor and Ronald Waterreus was able to save.
Rangers made the points safe when Novo outpaced Fagan leaving Arveladze to slide home his cross.
Buffel added a fourth when Marshall failed to clear and Prso's pass found the Belgian who drilled his shot low into the net.
Motherwell gained a late consolation when Clarkson's cross was missed by Waterreus and Andrews could only deflect the ball into his own net.