Germany were already a goal down to their European neighbours when they walked out for half-time.
And moments into the second half, Sane saw red as he reacted angrily to a foul from Mwene.
As the 29-year-old went to confront him, the former Manchester City star launched up from the ground and pushed his opponent over.
He did so by pushing both of his hands into Mwene's face in an aggressive fashion right in front of the referee.
It capped off a miserable night for the Euro 2024 hosts as they suffered a 2-0 defeat.
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Former Manchester United star Marcel Sabitzer opened the scoring for Ralf Rangnick's side by netting in the first-half.
Christoph Baumgartner then doubled Austria's score in the 73rd minute with a sublime chip over Kevin Trapp.
Germany are already in next summer's tournament as hosts but manager Julian Nagelsmann has come under some pressure following a defeat to Turkey last weekend.
But they have been in problematic form for some time now before Nagelsmann took charge.
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Hans Flick became the first manager to ever be sacked by Germany after Japan thrashed them 4-1 in September.
After two years in the role, he departed with the second-worst points rate with 1.72 with 12 wins out of 25 games.
At the World Cup in Qatar, they were eliminated at the group stage for the second tournament in a row.
Nagelsmann has somewhat improved their form after a win against USA last month and a draw against Mexico.
But defeat to Turkey and a poor performance to Austria on Tuesday night has seen morale plummet once again.
The ex-Bayern Munich boss signed a one-year deal with Germany after taking the job on 22 September.
It will see him take charge of Die Mannschaft for Euro 2024 with his future likely to be decided based on how they fare.