LAS VEGAS — With a pair of rear naked chokes that finished two celebrated champions, Nate Diaz and Miesha Tate both accomplished the improbable in a pair of sport-shaking victories at UFC 196. Diaz forced Conor McGregor to tap out with 48 seconds left in the second round Saturday night, ending the Irish superstar’s 15-fight winning streak in a non-title bout. Tate won the UFC bantamweight title at the MGM Grand Garden Arena, locking Holly Holm in a choke that rendered the champ apparently unconscious with 90 seconds left in the fifth round. The dual upsets stunned a sellout crowd and one of the biggest pay-per-view audiences in the history of mixed martial arts. They also threw two potential wrenches into the UFC’s plans for the upcoming year: McGregor was widely expected to fight in the main event at UFC 200 in July, while Holm’s next fight was supposed to be her rematch with Ronda Rousey, whose title reign ended with Holm’s knockout win in November. Diaz and Tate had plans of their own. “After 16 years in this business, the one thing you don’t ever do is think you know what’s going to happen,” thrilled UFC President Dana White said.