Having been a crucial cog in the Yeovil side since joining three years ago, Upson knows what the 2-1 aggregate victory over Sheffield United means to the football club.
They are now just 90 minutes away from their first ever promotion to the Championship, just 10 years after ending their 108-year non-league exile.
And the former Ipswich trainee admits his glancing header from Paddy Madden's cross was an emotional moment.
He said: "I could have kept running after that goal, I could have run straight out the stadium and run home. There was a bit of a tear in my eye. There were all sorts of emotions.
"I can't get my head around it just yet, it is something I'll have to go home and sit and think about for a while.
"My first ever header was earlier this season against Wycombe in the cup but they are a rarity and a great time to produce something that rarely happens.
"It is the most important goal I've ever scored in the biggest game I've ever played in, so to do that was special for me. I will hopefully score a more important goal in two weeks' time - the winner."
While Upson has chipped in with six goals this season his fine through ball for Kevin Dawson's opener was his tenth assist.
His role in both goals was the perfect response after Gary Johnson's disappointment at elements of his game in the 1-0 first leg defeat.
"I remember the pass for the first goal clearly, that was really satisfying and I loved it," he explained.
"Kev made an unbelievable run which made my mind up about where to put the ball. It was such a calm finish from him.
"The manager was a bit unhappy with something that happened on Friday so to give him that sort of performance with an assist and to score is the reaction he was looking for."
Yeovil have reached the third tier play-off final once before, under Russell Slade back in 2006/07, where they lost 2-0 to Blackpool at Wembley.
And Upson paid tribute to the thousands of supporters that invaded the pitch at the final whistle who are now planning their trips to the capital looking to watch their side make history and prove people wrong once more.
"It (the pitch invasion) was brilliant and ridiculous," he said. "I looked one way and was so pleased then I opened my eyes and the next thing I knew there were 15 people in my face.
"To celebrate with them after the game was so good because they were brilliant. Their support was really top notch and this is for them really because they deserve it.
"We are just so confident to be honest. We know if we play our game we are a tough match for anyone.
"I know it seems like we are a little club to the outside world with one of the lowest budgets but look who we have proved wrong. we are always favourites to go down and we are in the play-off final."