Southern beat defending champion Alhambra-Union 20-19 in the semifinal at the University Oval.
It was a special moment for Belcher, the host of the Shiel Hill Tavern, because the rest of his week had been filled with sadness.
Regan McCormack, the son of Belcher's partner, Kay, drowned in the Otago Harbour on July 10.
"It's been very hard for Dave this week. But he was jumping up and down for joy after that try," Southern coach Daryl Paterson said.
"It was great for me and the boys in the team to put a smile on his face."
Belcher was joined by his partner at the game.
"Kay's world has been ripped apart since the accident," Paterson said.
"If our win today made them both feel better, I'm happy about that."
Southern will play Dunedin in the final at Carisbrook on Saturday.
Dunedin beat Pirates 21-7 in the other semifinal at the University Oval.
Southern has won the banner 21 times, the last occasion being in 2007, when it beat Dunedin 13-9.
Dunedin has won the banner nine times and is seeking its first title since 2005, when it beat University A 19-12.
This will be the fourth time in five years that Dunedin has been in the final.
It lost to Alhambra-Union (26-10) last year.
