Di Grassi had been running in eighth place during a safety car period, which was instigated by Antonio Felix da Costa being eliminated by Porsche driver Andre Lotterer into Turn 1.
As the safety car slowed on the approach to da Costa’s stricken DS Techeetah car, di Grassi hit the 50km/h-limited pitlane and attempted to stop in the Audi box before rejoining in the lead of the race.
Due to the leisurely safety car pace and the short pitlane at the ExCeL Centre, di Grassi climbed seven places and resumed ahead of long-time leader Stoffel Vandoorne.
He remained in first place on the road as he ran across the finish line after 30 laps but was hit with a black flag.
This relegated him to eighth in the provisional results.
However, di Grassi was not informed by his team that he had been given a drive-through penalty for failing to stop completely in the pitbox, having locked up on the slippery indoor surface.
He has now been fully excluded, while Audi must pay a suspended €50,000 fine – only €5,000 is due straight away – for failing to inform its driver.