McDonald pulled the secondary together for a players' only meeting and told them Garza's abrupt exit did not erase all the time they had spent preparing and would not hurt their on-field performance.
"T.J. was just telling us we are a family, we are Trojans and he will keep leading us and putting in hard work and effort," cornerback Nickell Robey said. "When T.J. let us know how he felt about it, it just made everybody comfortable knowing that we weren't the only one feeling the same way.
"We just had to use this as a stepping stone and not let the adversity kill us."
With graduate assistant Sammy Knight and assistant head coach Monte Kiffin taking over Garza's duties, USC limited the Golden Gophers to 192 yards passing and corner Torin Harris came up with an interception in the final minute to secure the victory.
Knight credited both Garza for preparing the group, McDonald for steadying them and "setting the tone."
"I know Willie Mack was a great defensive backs coach and he had them prepared this week," Knight said. "It's my job next week to have these guys ready to roll."
CBS Sports reported that Garza was moved out after a relationship with Texas-based scout Will Lyles that predated his time at USC was disclosed in a meeting last week with NCAA investigators.
Lyles is under investigation for his ties to numerous programs including Oregon and LSU.
No one was exactly clear as to the nature of the "personal reasons" for his resignation Garza cited in a statement.
"I was shocked at first," McDonald said. "I didn't know what happened. I mean it was just one day you're here, next day you're gone."
"The bottom line was it's just like football," Knight said. "Something happens, we move on and go to the next play."
USC head coach Lane Kiffin did not say how he would replace Garza, but all indications are Knight will continue to oversee the defensive backs for the remainder of the season.
Knight, who played safety and linebacker at USC from 1993 to 1996 and in the NFL for 12 years, would obviously like to be considered for the vacancy.
"I would love to throw my hat in the ring, but that's a Lane Kiffin decision," Knight said. "Whatever he decides, I support the USC Trojans and the Trojan Family. That's out of my control. All I want to do is help these DBs get better as an assistant right now."