Ajax were gunning to make the UEFA Conference League with Marc ter Stegen in goal for his first European match with the Amsterdam outfit, while Marcos Leonardo filled the striker position and Oscar Gloukh and Julian Brandt started together for the first time.
After Leonardo squandered a promising opportunity in the opening phase, Sion got the biggest chance of the first 15 minutes via Winsley Boteli, who hit the post
After a period of slight pressure from Ajax, Sion surprisingly took the lead after 34 minutes, with Franck Surdez free to fire the ball into Ter Stegen's far corner after a cutback from Ali Kabalcaman.
Ajax were lucky not to concede another goal before the break when Numa Lavanchy's shot was touched and saved by Ter Stegen.
Julian Brandt saved Ajax shortly after half-time, picking up a cleared cross and firing the ball into the top corner to find a much-needed equaliser and inject some life into Michel Sanchez's side.
As much as Ajax needed the equaliser, 20-million-euro striker Marcos Leonardo needed his first Ajax goal to get off the mark. Within the hour, the Brazilian got exactly what he needed, heading in a lofted ball from Anton Gaaei to give Ajax the lead in the Swiss Alps.
Sion found themselves back in Ajax's box and got a penalty after Boteli went down as he felt the hand of Jorthy Mokio on his shoulder. Following a quick VAR check, Ilyas Chouaref stayed ice cold and converted from the spot with 15 minutes remaining.
It was an up-and-down second half in Sion, which took another turn when Nigerian striker Tolu Arokodare scored one minute after coming on for Leonardo, heading the ball diagonally past Anthony Racioppi.
Ajax captain Davy Klaassen concluded the second-half turnaround with a lob, assisted by Tolu in the 86th minute.
It was the final act of Ajax's comeback, which saw them score four goals in the second half to return to Amsterdam with a two-goal lead in hand. Ajax will host FC Sion in the Johan Cruyff ArenA on Thursday, August 27th.
Check the full match statistics on Flashscore
