"Flyweight division, say hello to your worst nightmare," one commentator said as the "Bullet" raised her arms in triumph.
But before celebrating too heartily she bent down to check on her bloodied opponent who showed no signs of getting up.
Fans, fighters and members of the UFC media were at a loss to explain why referee Mario Yamasaki did nothing to stop the bloodbath when it was clear Cachoeira was unable to protect herself.
UFC president Dana White slammed the refereeing, venting his anger in an Instagram post after the fight.
Yahoo Sports UFC writer Kevin Iole was another to blast the referee's "sickening" failure.
Some commentators even branded the officiating of the fight "criminal".
While the refereeing was questionable, there was no doubting Shevchenko's effectiveness in the Octagon. After suffering a controversial split decision loss to Amanda Nunes at UFC 215 in September, she returned to action with a point to prove.
Earlier, Santos opened up the main card with an emphatic win over Smith. He had the higher work rate and landed blow after blow on the American, who did well to stay in the contest for as long as he did.
They both let their hands go at the end of the first but Santos landed first and dropped Smith, opening up a gash.
Early in the second the Brazilian landed a solid kidney kick that rocked Smith and he unleashed with a barrage of strikes, forcing the referee to stop the fight.
Alcantra took just over a minute to dismantle Soto, pummelling him up against the cage to secure his rapid win.
MAIN CARD
Lyoto Machida defeated Eryk Anders via split decision (48-47, 47-48, 49-46)
Valentina Shevchenko defeated Priscila Cachoeira via submission (R2, 4:25)
Michel Prazeres defeated Desmond Green via unanimous decision (30-27, 29-28 x2)
Tim Johnson defeated Marcelo Golm via unanimous decision (30-27, 29-28 x2)
Douglas Silva de Andrade defeated Marlon Vera via unanimous decision (30-27 x3)
Thiago Santos defeated Anthony Smith via second-round TKO (1:03)
UNDERCARD
Sergio Moraes defeated Tim Means via split decision (28-29, 29-28 x 2)
Alan Patrick defeated Damir Hadzovic via unanimous decision (30-25, 30-27 x 2)
Polyana Viana defeated Maia Stevenson via submission (R1, 3:50)
Iuri Alcantra defeated Joe Soto via first-round KO (1:06)
Deiveson Figueiredo defeated Joseph Morales via second-round TKO (4:34)