It paid massive dividends on Friday night as they survived an early scare from Carlton and broke clear after halftime in their AFL elimination final at the MCG.
With Bailey Smith struggling to shake Cooper Lord's tag in the first half and Max Holmes short of a gallop in his return from injury, Mannagh was the Cats' firestarter as they kicked six goals to two in the pivotal second term.
In his third season as a mature-age rookie recruit, the 29-year-old is a classic case of never giving up.
He was named the coaches' association best "young" player last year, and had become a mainstay in the Geelong attack.
But as the finals loomed, and with Holmes injured, Mannagh started spending more time in the midfield and he relished the opportunity.
Early in Friday night's clash, it looked like Sam Walsh would be the midfield star as he continued his outstanding form.
But Mannagh was holding his own and pounced at the start of the third quarter, kicking a goal in the first minute.
It put Geelong in front for the first time since the opening quarter.
As Smith broke Lord's shackles, Mannagh racked up 11 disposals and two clearances through the third term.
What looked like a line-ball game had become 21-point lead at the last change.
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