Haller, who joined the Amsterdam club in January 2020, was a huge flop for West Ham in the Premier League, hitting just 14 goals in 54 appearances following his huge £45million transfer from Eintracht Frankfurt.
But it's been a different story for his new club.
He's hit a remarkable 29 goals in 40 appearances for the Dutch giants and left Hammers fans livid that he didn't enjoy the same form in England.
He scored twice for Ajax in the second half to turn the game around for his side after they fell behind in the 22nd minyte.
In finding the net, Haller joined an illustrious group of players to hit five goals in their first five appearances in Europe's elite competition.
He became the fourth player to complete the feat, after Alessandro Del Piero (1995), Diego Costa (2014) and Erling Haaland (2019).
Haller admitted to talkSPORT earlier this year that a move to Ajax was right for both parties as he explained his West Ham struggles.
"At the time it was a good step to go to West Ham. The people were nice to me and the project is why I decided to move," he said.
"After one-and-a-half years It was the best solution for both parties to separate.
"It's never easy to understand why it was not going well and it was not perfect for me the situation in the club."