USC safety Isaiah Pola-Mao, a redshirt freshman, has a week to remember

When Nevada Las Vegas running back Lexington Thomas faked a reverse handoff and streaked down the sideline for a 71-yard touchdown run to give the Rebels an early 7-6 lead over USC on Saturday, the knee-jerk reaction was to take it as a sign that the Trojans had not improved from a year ago at limiting big plays.

In actuality, what happened on the play was more complicated than that. The explanation begins with a phone call last week from sophomore safety Bubba Bolden to his good friend, redshirt freshman safety Isaiah Pola-Mao.

Bolden had won the starting strong safety position in fall camp, thanks in part to the surprising departure of their teammate, Ykili Ross, to concentrate on his upcoming graduation so that he could become a grad transfer in the spring. Bolden was riding high, telling reporters at Wednesday’s practice that he wanted to be a leader on the defense and eventually, a team captain. With Ross now out of the picture, Pola-Mao was Bolden’s backup. Pola-Mao was unprepared for what Bolden had to say:

Pola-Mao was going to start in Bolden’s place Saturday.

“He wanted to tell me before I heard it from the coaches,” Pola-Mao said. “Me and Bubba are really close. Hopefully he gets through it all.”

USC coach Clay Helton has kept Bolden’s situation a mystery. All he would say last Thursday publicly was that Bolden did not practice that day and would not be available Saturday due to a personnel matter.

“I was overwhelmed with a lot of emotions,” Pola-Mao said. “I was very sad for what Bubba was going through. I had to lock in and just focus and clear my mind.”

Pola-Mao, a 6-foot-4, 200-pound safety from Phoenix, came to USC with a lot to live up to beyond his four-star prospect rating. His father, Tracey, played at San Diego State. Bigger than that, his uncle is former USC and Pittsburgh Steelers great Troy Polamalu. But Saturday was still his first game in the Coliseum, and suddenly, he was starting.

“Very anxious,” he said. “I needed to get the jitters out.”

Friday night, Pola-Mao had a feeling that he was going to make a game-changing play.

“I felt it in my heart,” he said.

On the first play of the season for the USC defense, Thomas carried the ball into the trenches, and there was Pola-Mao, playing up, tackling him and poking the ball out for a Porter Gustin fumble recovery.

Unforgettable.

Later in the first quarter, with USC leading 6-0, UNLV called that fake reverse handoff. In the Trojans’ alignment for the play, Pola-Mao was supposed to stay on the left side of the field. As the play developed, though, “I heard somebody saying, ‘Reverse! Reverse!’” he said.

Pola-Mao took off to his right. Thomas went left and didn’t stop until he found the end zone and silenced the Coliseum.

“I tried to just overdo it and do other people’s jobs,” Pola-Mao said. “Now I know I just have to focus and do my own job because I know everyone else will do theirs.”

Pola-Mao finished the day tied for the team lead in tackles with seven. On Sunday night, Helton said there was no change to Bolden’s status, so this is Pola-Mao’s job.

He was one of a handful of Trojans who were making their first start defensively in their college debut, along with defensive tackle Jay Tufele and cornerback Greg Johnson. It was a day for the defense as a whole to get the jitters out. So to see that long touchdown run by Thomas and assume that it said something larger about the state of the USC defense in 2018 would have been a classic Week 1 overreaction.

“He was one of those kids that were out there for the first time as a redshirt freshman,” Helton said. “He had a mistake or two that we’ll learn from. But for the first time out, I was very pleased.”

More data will become available soon — on Pola-Mao and the USC defense’s recent penchant for giving up the big one — with road games at Stanford and Texas the next two weeks.

“I feel like we all believe we are the best defense in this conference and in the nation,” Pola-Mao said. “It just takes the little things. Sometimes, as it shows, the little things matter.”

brady.mccollough@latimes.com

Twitter: @BradyMcCollough