Trainer Lance O'Sullivan made the decision to bring the talented stayer back to New Zealand after a disappointing effort in Wednesday's A$150,000 Geelong Cup.
In what was to be his final Melbourne Cup lead-up, Pentane settled back last in running and passed a handfulof beaten horses in the home straight.
"Although we were happy enough with him going into the race, not everything has gone right and we're bringing him home to spell him," said O'Sullivan.
"He'll live to fight another day."
Pentane, the winner of this year's Auckland Cup, had been heavily backed to win the Melbourne Cup almost from the start of betting.
With the New Zealand TAB, Caulfield Cup winner Tawqeet remains the Melbourne Cup favourite at $5, just shorter than the $6 about Irish stayer Yeats.
"Yeats is definitely the one the public have grabbed hold of," said Melbourne's Domebet bookie Brian Taylor.
"We've had to bring him in from $7 to $6."
New Zealand stayer Mandela has dropped into $20 for the Melbourne Cup after winning the Geelong Cup.
