LOS ANGELES -- USC head coach Lincoln Riley said Monday that the decision to fire defensive coordinator Alex Grinch with two games left in USC's regular season was made in large part because the Trojans still have "a lot to play for" this year.

"We simply weren't making the progress I think we all expected to make," Riley said. "It just felt like it was in the best interest of our program."

At 7-3 and 5-2 in conference play, USC would need to beat Oregon and UCLA in its last two matchups and receive some major help from its conference counterparts to make it to the Pac-12 title game for the second straight season under Riley. But, as the second-year coach expressed a belief that the Trojans are "two snaps" from being undefeated, he remained adamant that they still have a shot at turning the season around.

"If we were in a situation where we didn't have a whole lot left to play for in terms of a conference championship, [I] might feel a little bit different," Riley said of the decision. "But we are very laser focused on these opportunities ahead, and then whatever comes next after that, we'll deal with it at the appropriate time."

One source close to the program told ESPN that pressure from two of USC's biggest donors also played a factor in the timing of the move. But when asked Monday if anyone else had any input on the decision to fire Grinch, Riley shot the notion down.

"It was my decision," he said.

Riley said that he rewatched USC's 52-42 loss to Washington Saturday night and lost sleep over the decision before reaching a conclusion on Sunday and relieving Grinch of his duties. Grinch, who was Oklahoma's defensive coordinator from 2019 to 2021 before leaving for USC alongside Riley, led a unit that allowed an average of 34.5 points per game this season and was in the bottom 30 in the country in nearly every statistical category, including 120th in rushing defense and 107th against the pass.

"I knew it was a decision that was the right decision at this time and point, but certainly didn't make it easy," Riley said. "But I am that committed, and we are all that committed to playing great defense here, and whatever it takes to get that done, that's what we're going to do."

Going back to last season, when USC finished the year allowing 47 points to Utah in the Pac-12 title-game loss and 46 points to Tulane in the Cotton Bowl defeat, Grinch had been the subject of much criticism surrounding his and the unit's performance. Throughout the offseason, USC, Grinch and Riley specifically preached patience and gave an optimistic outlook on the progress the defense would make with more time and more talent.

Yet even as USC used the transfer portal to bring in defensive players such as former Georgia lineman Bear Alexander and ex-Oklahoma State linebacker Mason Cobb, the performance of the unit did not improve. USC finished last season as the 87th-ranked team in defensive SP+. This season, it again is ranked 87th.

Until this weekend, Riley had stood by Grinch, whom he called "a friend" on Monday and praised for being the first assistant to agree to follow him from Oklahoma to USC.

"[We're] not laying all the blame at Alex because the reality is I have a role in that," Riley said. "The other defensive assistants have a role in that. Our players have a role in that. Our other staff members, everybody has a role in it. And so if it goes well, that's great, and if it doesn't go up to the expectations then changes are going to be made, adjustments are going to be made, and that's just part of the business."

As the Trojans head to the Big Ten next season, likely without reigning Heisman winner Caleb Williams, the task at hand to revamp and improve the defense will be no small feat. On Monday, Riley did not want to dive into exactly what he will be searching for in a new defensive coordinator, but he was staunch in his belief that the program will get the best person for the job.

"Nothing will trump getting the right person in here because we're going to play great defense here, period. It's going to happen. It's going to happen soon," Riley said. "There's not a reason in the world it can't. We'll continue to take the steps we have to do it, and we're going to be very aggressive that way."