All it took was one, quick glance out of the corner of his eye for Kobe Johnson to know what was about to happen next.

USC was clinging to a four-point lead with less than three minutes remaining Thursday night at Galen Center when Johnson spotted Washington State’s Carlos Rosario moving toward the hoop. Johnson reacted instantaneously, leaving his man to arrive a split second before Rosario, intercepting the pass at the game’s most critical juncture.

It was precisely the sort of heady play the Trojans have come to expect from their 6-foot-6 sophomore stopper wing, whose instincts have made him essential to USC’s defensive identity. Coach Andy Enfield didn’t hesitate Thursday night to anoint Johnson as “the best defender in the Pac-12.”

“He read the cutter. That was an incredible steal,” Enfield said of Johnson’s clutch play during the Trojans’ 80-70 victory. “To see that cut happen, then go and steal the ball, was probably the biggest play of the game.”

For Johnson, it was nothing out of the ordinary. He had already earned a reputation at the Trojans’ practices for being a defensive menace, with an uncommon ability to anticipate passes before they happen.

“He’s always trying to cheat the play and be in the passing lanes,” point guard Boogie Ellis said. “He’ll hide behind a big and then come out of nowhere to get the steal. And it’s like, ‘Dang.’ That’s Kobe.”

In that regard, few in the nation have been better at defending the perimeter this season. Johnson’s 4.6% steal rate ranks 23rd in college basketball. Against Washington State, he helped hold TJ Bamba, the Cougars’ top scorer, to one of his worst shooting performances of the season (two for 10, seven points).

Although his defensive prowess has been prolific this season, Johnson has yet to make much of a mark on the other end. He has taken just 14.3% of USC’s shots while he’s on the court, a rate that ranks second lowest among guards in the Pac-12 Conference. Until the final minutes Thursday, Johnson had yet to attempt a shot.

That fact didn’t seem to bother Enfield, who shook off a question about whether Johnson could be kept on the floor without providing much offense. He added that Johnson had been battling an ankle injury.

“I don’t care if Kobe scores a point,” the coach said. “He just helps you win in so many areas.”

On Thursday, he even eventually helped the Trojans’ offense. With less than four minutes left, Johnson stood uncovered beyond the three-point arc. When the ball found him, he didn’t hesitate to let a three-pointer fly, sinking the shot that would give USC the lead for good.

Josh Morgan will miss USC’s game Saturday night against Washington (13-11, 5-8 Pac-12) at Galen Center after he suffered an ankle injury Thursday, a person familiar with the matter who was not authorized to speak publicly about the injury told The Times. Whether that injury is more than just a bad sprain was uncertain Friday.

With Morgan out for at least one game, freshman 7-footer Vince Iwuchukwu is likely to make his first college start for the Trojans (16-6, 8-3). Iwuchukwu has played in just six games this season since he returned from a traumatic episode last summer in which he suffered cardiac arrest.

Iwuchukwu remains on a minutes restriction as part of his recovery from that incident. He played a season-high 22 minutes Thursday and isn’t likely to play much more than that in the coming games as USC continues to bring him along cautiously.

But he will have to take on a bigger role while Morgan is sidelined, as will fellow big men Kijani Wright, Harrison Hornery and Iaroslav Niagu, none of whom have more than a few college games under their belt.

“We have a lot of inexperience, but I think they’ll be up for the challenge,” Enfield said. “They have to get ready to play.”