Nigeria international and Slavia Prague striker, Peter Olayinka, scored a first-half header, which gave the Czech champions the lead following a 1-1 draw in Prague.
Nicolae Stanciu doubled the advantage after another Nigeria international, Rangers’ Leon Balogun, was shown a second yellow.
Rangers were already down to 10 by then, Kemar Roofe having been sent off within six minutes of coming on for catching goalkeeper Ondrej Kolar in the face with his boot.
There was still time for further tumult in the closing minutes. A strong challenge by Connor Goldson precipitated a melee, and Ondrej Kudela uttered something to Glen Kamara while covering his mouth with a hand.
That enraged Rangers’ players, with Kamara, Goldson and Bongani Zungu particularly incensed, and manager Steven Gerrard confirmed afterwards that Kamara told him he was racially abused, with other players also having heard the comments.