When Greenock Wanderers were 35-11 up with less than a quarter of the match to play, it looked very much like the trophy was going to be heading to Fort Matilda.
However, the Scremerston side, inspired by former Scotland Sevens man Andrew Skeen, battled back to bring the scores level at 35-35 after 80 minutes.
They were then the team with the momentum going into extra-time and they duly ran out 50-35 winners to spark jubilant scenes at the national stadium.
A converted try from Gareth Hill was the catalyst for the Berwick fightback before Matt Gray was then yellow carded for Greenock. That gave Berwick space and they certainly made the most of it.
Another try from Hill, one from Euan Thompson and then one from Scott Owens, with Skeen slotting the conversion, took it into extra-time.
In extra-time, Skeen’s penalty made it 38-35 against the shell-shocked Wanderers, and when Ali Grieve scored a superb solo try it was 43-35. A Jack Dalrymple try converted by Skeen sealed the comeback of all comebacks.
Jackson said: “It was a great team effort, I’m so proud of the boys, I thought the bench had a massive impact.
“We won East League One, the regional Borders Shield and now we’ve managed to take the Shield home and it’s our 50th anniversary season. It’s absolutely massive for us.”
Aberdeenshire’s Tom Watson led the way with two tries as they claimed the Men’s Bowl earlier in the day by edging out Dundee Uni Medics 34-31.
Winning skipper Frazer Forman, who has seen his side win three trophies this term, said: “I think it’s the greatest season we have had in the club’s history.”
On the back pitches, Greenock Wanderers won the Women’s Bowl by defeating Livingston 72-12 and Stewartry Sirens just got the better of Glasgow University to lift the Women’s Plate 24-19.
In their match Greenock sent their departing coach Ally Hunter off in style as they ran in 12 tries, but it says something of the way that Livingston’s Leanne Moir took her two tries that she was named player of the match.
Four of the Greenock tries were scored by Catriona Cowan, with the Haldane sisters Caitlyn and Erin also amongst the scorers.
A late try from Claire Manson sealed Stewartry’s glory, the students leading until late on, but just being pipped at the post.