The Wigan midfielder only returned to action last weekend after almost six months out and did not make the starting line-up for Saturday's FA Cup final against Manchester City at Wembley.
But Watson got his chance in the 81st minute and 10 minutes later rose highest to head Shaun Maloney's corner into the top corner of Joe Hart's goal and seal a shock 1-0 victory.
Asked to consider his new position in British football folklore, the 27-year-old could only shake his head and laugh at the improbability of it all.
But Watson did reveal the opportunity to appear in an FA Cup final had spurred him on in his recovery from the broken leg he suffered in a challenge with Liverpool's Raheem Sterling in November.
The midfielder said: "It was a long six months but I worked hard and was around some good people. They helped get me through those six months and this is a dream come true.
"When we got to the final that was always my aim, can I get fit for the final? I did that, I worked hard. It definitely makes it sweeter. Breaking your leg to scoring the winner in an FA Cup final. It's crazy. I hope I never come down from this high."
Wigan's victory over last season's Premier League champions was far from a smash-and-grab raid.
Although Latics goalkeeper Joel Robles made three very good saves, Wigan caused the City defence no end of problems, with Callum McManaman coming close to opening the scoring on a number of occasions.
The forward twice forced Pablo Zabaleta into fouls that earned the City full-back a late red card and provided the impetus for Wigan to clinch their first major trophy.
Watson said: "No one thought we'd win but the lads believed, the fans believed and we've done it.
"We were under no pressure, Man City were under pressure to bring silverware back home. We knew we could go out there, enjoy the game, it's not like you're going to be in an FA Cup final every year in your career.
"I thought we controlled the game. We were creating good chances and I thought we were definitely going to win. The lads out there from the goalkeeper through to the forwards, everyone was fantastic.
"I just wanted to get on the pitch. Once I got on there and they went down to 10 men, I knew this was our chance to win an FA Cup."
The champagne is on ice, though, with Wigan facing a desperate fight to secure their Barclays Premier League future this week.
Instead, the Latics toasted their success with Irn-Bru - a favourite of their Scottish contingent - ahead of key fixtures against Arsenal and Aston Villa.
Watson highlighted the role played by manager Roberto Martinez, saying: "He's a positive man, so calm, the sort of guy you need in these situations. Hopefully we can pull it off for him again."
Defender Paul Scharner was the only member of the Wigan side who also played in their other major cup final appearance - a 4-0 loss to Manchester United in the League Cup final in Cardiff in 2006.
The Austrian returned to the club on loan from Hamburg in January until the end of the season, and he revealed what an emotional moment it was when he realised he would be leaving with an FA Cup winner's medal.
Scharner said: "I'm really happy that little Wigan won the FA Cup. It's indescribable to be honest. Nobody expected that Wigan would win. I cried for five minutes on the pitch."
Not the least of the surprises on Saturday was that Wigan kept a clean sheet.
No team in the Premier League has conceded more than the Latics' 67 goals in 36 games, and two horrible pieces of defending cost them what would have been a vital victory against Swansea last week.
Scharner said: "As a defender you are always disappointed when you concede but football is a team sport and you need to defend together, like we did, and you need to attack together. I hope we can keep these positive feelings over the next two games."