Chrisean Rock wasn't inside the ring Saturday night ... but she took her sister Tesehki's loss like it was her own.

Chrisean livestreamed herself watching the fight and became increasingly emotional as Big Lex took control ... eventually breaking down in tears. At one point, she turned to her viewers and asked, “Why do I feel like I lost?”

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Big Lex ultimately defeated Tesehki by unanimous decision after three rounds at Atlanta’s State Farm Arena ... winning all three judges' scorecards and claiming the "Baddies" championship.

At one point in the stream Chrisean hints at the fact that she doesn't even talk to her sister, but she is still shattered by Tesehki's loss.

The bout aired as part of the undercard for Claressa Shields' middleweight title fight against Kaye Scott ... with Kim Kardashian among those watching the action in person.

Chrisean's emotional night comes just days after her baby daddy Blueface had cops called to his Santa Clarita home over another live stream.

As TMZ previously reported ... deputies responded after Blueface was seen kicking his pregnant girlfriend Nevaeh Akira into a pool. Nevaeh told authorities there was no altercation and she wasn't injured, so no arrest was made.

Rough night for Tesehki ... and judging by Chrisean's reaction, the loss landed twice.