The Space Stone acted as the first time an Infinity Stone is present in the MCU, albeit not shown as an Infinity Stone. It appeared in Captain America: The First Avenger in the form of the Tesseract. It was portrayed as a blue cube that Hydra leader Red Skull used to create super-powered weapons and tech.
This may be a bit of a low blow as it was achieved using tech from the forties, but given the abilities of the Space Stone making laser cannons seems like a bit of a wasted opportunity. The Space Stone’s powers grant the user the ability to travel through space via teleportation, which has been seen twice in the MCU yet never formally acknowledged.
Red Skull inadvertently utilises it towards the end of Captain America: The First Avenger, when he grabs the Tesseract with his bare hands. Given the context seen throughout the film, the bright light and beam into the sky seemed to suggest that Red Skull was obliterated by the Tesseract, yet it’s true nature is revealed at the end of The Avengers (or ‘Avengers Assembled’ for us in the UK) when Thor and Loki use it to teleport back to Asgard.
The question remains; where is the red faced Hugo Weaving? Well, given that he publicly lauded the experience of being in a Marvel film the Space Stone probably took him somewhere far, far away from Marvel's casting directors.