Despite leading 2-0 during the game, the Oranje bottled the lead but still found the game-winning goal late in the game.
De Boer has been heavily criticised by the Netherlands' fans as the team haven't really impressed since Koeman left them for Barcelona.
Later on Thursday, the Netherlands will take on Austria on Matchday 2.
Ronald Koeman won 11 out of 20 games with his national side as manager, leading the team to the Nations League final.
How Dutch boss De Boer 'made sure' Wijnaldum will earn a lot of money – but at PSG and not Barca
Indeed, a few days before Wijnaldum snubbed Barca for PSG, it was reported that Frank de Boer didn't let his players pass the medicals with their new clubs.
Koeman: 'Laporta knows I'm the best man for Barcelona'
Many Blaugrana fans were waiting for Xavi to be in charge of the team starting from the next season. However, after Laporta supposedly had negotiations with some other candidates, he preferred to stick to Koeman.
Earlier this month, Joan Laporta announced Ronald Koeman's stay. The Dutchman may soon sign a new deal that could potentially keep him at the club until 2023.
Koeman has been in charge of Barca since August 2020, leading the team to the Copa del Rey glory.
The 58-year-old has won 2.09 points per game with Blaugrana.