Short-term memory. Coaches stress it — and UCLA needed it Saturday in its home opener against San Diego State.

After his team reached the red zone only once in the first half — on a drive that culminated with an interception near the goal line — Bob Chesney probably wanted to forget about how the Bruins played in the first 30 minutes of his coaching debut at the Rose Bowl.

Fortunately for Chesney, he can feel better about how UCLA performed in the second half.

Scoring all of their points after halftime, the Bruins defeated San Diego State 28-10 to remain unbeaten on the young season.

After two games, the Bruins have outscored opponents 49-17 in the second half and 42-10 in the fourth quarter — a testament, Chesney said, to the team’s adaptability and cohesion.

“A lot of that has to do with adjustments that we can make, but then also our guys figuring out the speed at which things are happening,” Chesney said. “I’m not saying this as any excuse, but when you have 60 new guys on the team, that ability to jell together and play together early in the season, it takes a second, and you settle down when you get to halftime. You understand what the test is at hand, and then you really begin to trust one another and play together as a team.”

UCLA quarterback Nico Iamaleava struggled in his return to the Rose Bowl, completing 14 of 22 passes for 151 yards and an interception — giving him two turnovers and zero touchdown passes through two games.

Iamaleava’s costliest mistake came at the start of the second quarter when, rolling out to the right, he attempted to throw off his back foot to tight end Harry Lodge in the end zone, only to be picked off by San Diego State cornerback Mike Lindsay.

With starting wideouts Mikey Matthews and Landon Ellis sidelined, it was senior Semaj Morgan who rose to the occasion, the Michigan transfer hauling in six catches for 73 yards and setting up the Bruins’ first touchdown with a 25-yard punt return.

UCLA quarterback Nico Iamaleava attempts to break free from a tackle by San Diego State linebacker Tano Letuli.

UCLA quarterback Nico Iamaleava attempts to break free from a tackle by San Diego State linebacker Tano Letuli during the first quarter.

(Ronaldo Bolanos / Los Angeles Times)

“Semaj Morgan — that kid deserves a ton of credit for today’s game because there were plays that needed to be made, and he made them, and just in tight, contested areas, that kid is tough,” Chesney said. “Along with his punt return, along with his run blocking, it was really good to see him have the day that he had.”

Although the passing game has yet to take flight, the Bruins’ ground attack shined with 214 yards and four touchdowns. Fifth-year tailback Wayne Knight led the way again, scoring three touchdowns for the second straight game as he rushed for 97 yards on 13 carries.

“What does he mean to us? He means everything,” Chesney said. “He’s just a kid that is tough. He’s physical. He plays football the right way, and I love watching him be patient, and then he waits for it, and when he sees it, he just gets up to full speed within two or three steps. That’s nothing we haven’t seen before.”

Senior running back Jaivian Thomas also scored for the Bruins, matching his touchdown total of last season.

Iamaleava also was effective on the ground, running for 57 yards in 13 carries and earning multiple hard-fought first downs.

Chesney said the passing struggles against the Aztecs were largely a byproduct of the Bruins losing their top three receivers in the middle of the game, but added that the offense needs to adjust better.

“He knows it’s not his best game,” Chesney said of Iamaleava, “and again the grit and the toughness that he played with, when he needed to get a couple first downs that really mattered to keep drives alive and put his body on the line and peeled himself off that ground and kept fighting for his teammates, that’s special.”

While the UCLA offense failed to ignite until the second half, the “Bruin Bullies” enforced their will on San Diego State from the start.

The Bruins held Aztecs quarterback Jayden Denegal to 45 yards on six-for-17 passing — the second-fewest yards he has passed for as a starter. Denegal challenged outside cornerbacks Scooter Jackson and Rodrick Pleasant to no avail.

Linebacker Jalen Woods set up UCLA’s third touchdown by picking off Denegal in the fourth quarter for his first career interception — a play Chesney dubbed as “everything” at that moment of the game.

“Watching film, I know they like to take screens when it’s third and medium or long, and the back crossed, so it’s going to be a screen because he went right to left,” Chesney said.

The Bruins’ pass rush continued to create havoc, following their three-sack performance against California with two more and six tackles for a loss. The effort kept the Bruins in the game when Iamaleava was struggling.

“Coach Ches has done something special. These guys never waver; they always got my back,” Iamaleava said. “Defense always has my back, so it feels good to have that support cast coming from the defense, and then obviously our run game has been great for us.

“If we want to win these big games, I’m going to have to play way better, but it feels great to have a supporting cast that even if I don’t play the best, we can still pull out a win like this.”