Marvin Johnson struck seven minutes after the break, with the ball deflecting off Marius Zaliukas on the way into the net, and the Rangers defender later diverted Lionel Ainsworth’s shot past Cammy Bell before a late penalty from John Sutton secured a resounding 6-1 aggregate victory for Motherwell.
Victory ensures Well’s 30-year run in the top flight continues, while Rangers must toil again in the second tier, but the match was soured by unsavoury scenes at the finish.
A physical confrontation between Gers substitute Bilel Mohsni and Motherwell’s Lee Erwin sparked a mass brawl, while home supporters also flooded onto the pitch to taunt the visiting fans despite several warnings to remain in their seats.
Defending a solid 3-1 lead from the first leg of the play-off, Motherwell had seemed content to allow the visitors possession of the ball while maintaining their shape, and Rangers lacked the guile to break them down.
Motherwell dealt comfortably with a succession of high balls and long throw-ins as Rangers opted for aerial service to Kris Boyd, starting his first game since mid-March.
But it was Zaliukas who caused slight concern for the Steelmen in those early exchanges when he rose above his marker to meet a Nicky Law free-kick which forced George Long to tip the ball over the crossbar.
The game sprung to life after half an hour when Scott McDonald was inches away from getting his toe on a low delivery from Ainsworth as Motherwell finally got in behind the visitors with some swift passing.
Four minutes later Erwin created space just inside the Rangers penalty area and smashed a shot narrowly wide of the far post with Bell at full-stretch.
Stephen McManus then lost his marker at the edge of the penalty area and stooped to connect with a Johnson free-kick, and although Rangers ‘keeper Bell was flat footed the ball flew past the upright.
Motherwell came close again when Johnson and McDonald combined outside the box and the latter swept a dipping shot an inch wide of Bell’s left post.
At the other end Rangers squandered the best chance of the half after Keith Lasley got his head to divert a Shane Ferguson corner and the ball dropped to Zaliukas on the six-yard line, but he scooped it over the bar in what would be a defining moment in the game.
Richard Forster was almost caught out by Johnson three minutes after the break when he tried to step inside the Motherwell winger and had to make a recovering challenge inside the box.
But the breakthrough came on 52 minutes when Johnson weaved his way forward from the halfway line and past Lee McCulloch before he let fly from 25 yards, and the ball deflected off Zaliukas and looped towards the far post, dropping under the bar as Bell tried to punch clear.
McCulloch attempted the spectacular four minutes later when he sent a scissor-kick over the bar from a corner from substitute Nicky Clark, and Long caught a curling shot from Haris Vuckic at the second attempt shortly after that.
Motherwell killed the tie 20 minutes from time when Johnson raced forward from his own half and stepped inside McCulloch on the 18 yard line before rolling a pass to Ainsworth to smash a low shot which took a nick off the luckless Zaliukas with Bell diving in the opposite direction.
Bell kept the score down 10 minutes from time when man of the match Johnson again drove into the box and squared to Erwin, who spun his marker and although his shot was blocked substitute John Sutton followed up with a rebound which almost squirmed under the goalkeeper.
Erwin was tripped in the dying seconds by Lee Wallace inside the box and from the resulting spot-kick substitute Sutton showed his composure to send Bell the wrong way to complete the rout.
Following the full-time whistle Erwin pushed Mohsni and the Rangers defender responded with his fists and his boot before he was ushered off the pitch – both men, along with unused Well substitute Fraser Kerr subsequently sent off in the tunnel.
For all the late drama, Motherwell’s superiority over the two games was evident and Rangers must try again after their hopes of three successive promotions were dashed.