A former valedictorian of his high school, Gary Antuanne Russell (15-0, 15 KOs) passed the biggest test of his career with flying colors, stopping the former world champion Viktor Postol (31-4, 12 KOs) abruptly in the tenth and final round of their super lightweight bout in the SHOWTIME co-main event. After pushing the action for most of the fight, Russell hurt Postol with a left uppercut in the tenth and followed up with a series of lefts and rights. With Postol against the ropes absorbing combinations, referee Mike Ortega intervened and waived it off at 2:31 of the tenth, much to Postol’s surprise, who shrugged his shoulders and seemed miffed at the stoppage. Russell kept his knockout streak alive while Postol dropped his second straight contest. Russell was a 2016 U.S. Olympian who owned a 3-1 amateur record over current unbeaten welterweight Jaron Ennis, and he fought like one of the top contenders at 140 pounds on Saturday. “The performance speaks for itself,” said Russell. “Yo