By Daniel Teo
It was Tan's first silverware since taking over from Vorawan Chitavanich in January, but he was made to wait until the last five minutes of the game before goals from Alexandar Duric and Park Jo Seb sealed the win for the Stags.
But it looked to be going all wrong in his first competitive match when a new-look Etoile side got off to a dream start after 1.93m striker Jonathan Justin was alleged to have been brought down in the penalty area by Park in the ninth minute.
Midfielder Maxime Belouet duly converted the spot-kick to hand the French outfit an undeserving lead.
Speaking in a post-match interview, a visibly delighted Tan applauded his team's efforts and felt that the win will be a huge psychological boost in their bid to end a four-year trophy drought in the S.League.
Tan, who was nicknamed ‘Supersub' during his time in the Singapore national team, said: "Firstly, I would like to congratulate my boys, who played well and gave their all despite being one-nil down for most of the match.
"This will certainly give us confidence ahead of the new season as we look to bring the team to the next level.
"We are looking forward to the season and hopefully bring an end to our four-year trophy drought."
Asked to provide his reflection on the match, Tan admitted that his side were far from their best in the first-half but a half-time pep talk and coupled with Etoile's lack of match fitness helped the Stags to a resurgent second-half.
The 40-year-old added: "It wasn't the best of performance in the first-half as my boys were losing too much of the ball.
"But in the second-half we knew Etoile will struggle with their fitness as their players were hydrating whenever the ball went out of play. So I told my boys to up the pace of their game.
"We brought on Jamil [Ali] in the 82nd minute as we felt Etoile were sitting very deep and were compact in defence. So we needed someone who can take on the players one-on-one and he was the right man to do just that. And I am happy with the impact he made."
Tan went on to give his views on the ninth-minute penalty that was given to Etoile for an alleged foul on Justin Jonathan by Park and also the Korean defender's winning goal that clinched the Charity Shield for his side.
"For the penalty there was a tug from Park so I can have no complains about that.
"For Park's goal it could also have been a penalty as he was obviously fouled. But he chose to stay up and score the winning goal."
Despite dealing the champions an early blow, Tan refused to write off his French counterparts, as he is adamant they will only get stronger as the season progresses.
"Credit has to be given to Etoile as they are not an easy team to beat. I believe they will only get stronger as they are still getting used to the humidity and weather here.
"They have only just assembled the team so it will definitely take time for them to gel. So we can never write them off as I expect them to give the top teams a tough fight this season."
Finally, coach Tan was relieved to get a huge mental block out of the way with the Stags' first win over Etoile after two losses and a draw last season.
He concluded: "It is definitely a block off our shoulders and a huge mental boost going into the new season."
Tampines kick off their S.League season against Gombak United FC on 18 February at the Jalan Besar Stadium.