The Auckland side's 2-1 quarterfinal win over Dunedin Technical at the Caledonian Ground was no picnic, though.
The sides were locked at 0-0 after 90 minutes as a damp pitch made free flowing football near impossible.
The halves were split evenly between the sides, Mangere United creating the more chances in the first half, while Dunedin Technical looked threatening in the second half, largely through the set piece.
Former Auckland City player Sanny Issa was particularly elusive, using his speed down the right flank to good effect.
Once the game went to extra time, Issa stepped it up a gear, putting a shot on goal before midfielder Rinal Prasad cleaned up the loose ball to score and give the visiting side the advantage.
Dunedin Technical player coach Aaron Burgess came on at the end of regulation time, and his shot on goal two minutes after Mangere's score was chased up by striker Josh Stewart to bring the sides level.
However, a second yellow card for Technical's Ross Howard took the home side down to 10 men, and Mangere made it count when replacement right midfielder Shaneel Sharma got clear on the right hand side to score with a minute to go in the first period of extra time.
Mangere ran down the clock well in the second period to hold on, sending its 100 strong band of very vocal supporters into raptures at the final whistle.
Mangere coach Miroslav Nikolic described the side's progression to the semifinal stage of the Chatham Cup as the club's greatest success.
''In the end, I was very proud for our crowd who came down,'' Nikolic said.
''It was a pleasure to be here.
''We saw a small chance and we took it. I think we deserved to win.''
Both sides made substitutions as tired legs took over, and Nikolic praised his bench.
''We probably should have finished the game in the first half. In the second half, we struggled for the first 20 minutes. We did some changes and those people who came on helped us a lot.''
Burgess said he was proud of his side, which created several chances in the dying minutes of extra time.
''The boys gave it their all, still battling to the last minute for that equaliser,'' Burgess said.
''At the end of the day, it's cup football - it's do or die.
''They were really dangerous on the counterattack. I thought we blunted that well at times, but they always looked like they might get away on us at some point.''
Mangere will join Eastern Suburbs, Napier City Rovers and Birkenhead United in the semifinals.
Eastern Suburbs beat Cashmere Technical 2-1, Napier City Rovers overcame Western Suburbs 3-0, and Birkenhead toppled Central United 3-0.
Chatham Cup
The scores
Mangere United 2
Rinal Prasad, Shaneel Sharma
Dunedin Technical 1
Josh Stewart
Halftime: 0 0.
Fulltime: 0 0.
