Spurs reject Marcus Edwards was Man of the Match as Antonio Conte’s side were stunned by two injury-time Sporting goals.
The 23-year-old - tipped for an England call-up by boss Ruben Amorim - was allowed to leave Spurs in 2019 after being hyped up as a teenager. But he almost scored a first-half wonder-goal as part of an outstanding display.
Substitutes Paulinho and Arthur Gomes struck late to put Sporting in charge of Group D and Edwards said: “I could not be happier.
"We deserved that. We showed how we can play. I wouldn't say it was extra special but it was a strange feeling playing against Spurs. I was there for so long but it was good to know the people, the coaching staff and some players.
“It doesn't change. I prepare the same and focus like every other game.”
Asked about an England call-up, he added: “I wouldn't say it has crossed my mind. I just focus on what I am doing here so I don't think about that - but of course (it would be nice).”
But highly-rated Amorim, targeted by Chelsea before the new owners settled on Graham Potter, said of Edwards: “He has the talent and, as I said, he can make it to the English national team. He is an expensive player and he has a lot of talent for many years for Sporting.”
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Edwards joined Tottenham's academy at the age of eight and went on to sign his first professional contract at the club in 2016. He was then included in Tottenham's pre-season squad while boss Mauricio Pochettino likened him to none other than Lionel Messi.
But subsequent loan spells at Norwich City and Dutch side Excelsior followed before Edwards was allowed to move on after just one senior appearance for Spurs, joining Vitoria de Guimaraes on a four-year deal.
He managed to revive his career in Portugal before earning a move to Sporting in a deal worth more than £7million in January of this year, where he has flourished and put himself into the international picture. Edwards has represented England at several ages through the youth ranks from under-16 to under-20, though is also eligible to play for Cyprus due to his mother.
England boss Southgate may be persuaded to take a trip to watch Edwards in action after his mazy solo run in the first half where he left several Spurs players trailing in his path before forcing a save from Hugo Lloris. As it was, Sporting were able to earn victory thanks to two late goals from Edwards' teammates, but it was his performance that made the biggest impression.
Meanwhile Spurs will now have to pick themselves up again after their first defeat of the season. Conte said afterwards: “The Champions League level is high. You know that you have to reduce the mistakes because in the end you can pay.
“Here we paid a lot. Now we are talking about a loss against a team that showed they are used to playing this competition. But don't forget last season we lost against Mura in the Conference League and we made an important step forward.”