The senior center, who missed all but seven games last season due to a stress fracture in his foot, recorded his first double-double since 2010 in a 111-82 Ole Miss rout of Mississippi Valley State.
With the win, the Rebels moved to 3-0 on the year. They'll return to action Tuesday against North Carolina A&T.
"I was just waiting on that big game to come," Cox said. "I didn't know tonight was going to be the game, it just came at the right time. A lot of confidence going my way for the next game coming up."
Cox had two surgeries on his foot as a junior. His greatest contribution point-wise was a four-point effort against Lipscomb and McNeese State a year ago this month. His top rebounding total? Three.
Ole Miss head coach Andy Kennedy was proud to see the 6-foot-8, 276-pound Cox rewarded for his hard work. He finished with 15 points and 12 rebounds.
"I was really proud of Demarco Cox," Kennedy said. "He works so hard. I was glad to see him rewarded by finishing some plays at the basket."
Sophomore guard Derrick Millinghaus scored a career-high 21 points on 8 of 14 shooting from the floor. He also added two rebounds and three assists.
"Really good offensively," Kennedy said of the 5-foot-10, 172-pound Millinghaus. "Gave us great push. When he's in the game, we can get up and down the floor and make things happen in the open court."
Marshall Henderson, making his 2013-14 home debut, added 15 points on 4 of 11 shooting, with all of his makes coming from behind the 3-point line. Anthony Perez and Jarvis Summers contributed 14 points apiece.
The 111 points scored by Ole Miss were the most since the Rebels totaled as many in a win over Prairie View in 1998.
"We win the game, I got some guys hopefully feeling better about themselves because they play better," Kennedy said. "We've got to build and move forward."
Ole Miss won the rebounding battle, 43-37. The Rebels were good on 51 percent of their shot attempts, and they saw a drastic improvement at the free throw line, sinking 79 percent (30-38) of their attempts. They entered the game shooting 59 percent from the charity stripe.
"I thought we were tremendous early," from the free throw line, Kennedy said. "When you're up 25, 30 points, I understand it's hard to be on edge. It's hard to play on that edge. Overall, I was pleased with what we did."
Mississippi Valley State was led by Blake Ralling, who scored 16 points and grabbed four rebounds. Jordan Washington finished with 14 points.