Markel Brown and Le'Bryan Nash scored 16 points each as Oklahoma State won 73-65.
The Cowboys, coming off a 15-18 campaign, have battled injuries since last March. On Friday, two starters were freshmen and another, senior Jean-Paul Olukemi, had not played since an injury midway through last season.
UC-Davis, 5-26 last season, has a roster full of new faces.
"I told our team that I'm glad we won," OSU coach Travis Ford said. "This game could have gone either way, but I saw this kind of coming this week. We're so out of sync offensively right now. It was a product of us playing lineups tonight that we haven't even played in practice.
"Our offensive chemistry is not because of selfishness but because of everything we've been through during preseason."
Phil Forte hit three big shots in the second half and finished with 13 points for the Cowboys, who shot 40 percent from the field. Olukemi added 10 points for OSU. Freshman Marcus Smart had eight points and seven assists.
Corey Hawkins scored 13 points, Ryan Howley 11 and Josh Ritchart 10 for the Aggies.
The Aggies opened the second half on a 19-11 run and led 51-48 with 12:20 remaining.
A 3-pointer by Forte put the Cowboys up 53-51, and two free throws pushed the margin to seven points. UC Davis cut the lead to two when Tyler Les knocked down a three, and tied the game when Ritchart put back an offensive rebound at the five-minute mark.
But a score by Olukemi put the hosts up by two, and Forte's long-range 3-pointer in transition gave the Cowboys a 66-61 advantage a minute later.
The Aggies, who were 1-16 on the road last season, battled back on a pair of baskets by Howley and trailed by three when Forte hit a big jump shot for a 70-65 lead with 2:00 remaining.
"For us to come back in the second half and dig down deep to find a way to win was definitely a positive," Smart said. "Obviously, we have some negatives that we need to work on, but that's OK because it's the first game. Not everyone is meshing together yet with some players hurt, so we just kind of have to fix all that with practice."
Injuries have been part of the daily routine for the Cowboys. Brian Williams, a 6-foot-5 sophomore who averaged 9.6 points per game last season, injured a wrist during the preseason and will not return. Three of the squad's big men - Michael Cobbins, Philip Jurick, and Marek Soucek - have each missed significant time. Jurick played three minutes on Friday.
"Learning how to play without those (injured) guys and to gel in practice is something we are trying to (do)," Forte said.
Howley had 13 rebounds as UC Davis outrebounded the Cowboys 43-29.
"I was pleased with our scrappy effort, especially on the boards," UC Davis coach Jim Les said. "We battled. But give them credit because they hit the shots when they needed to. Their backs were against the wall and they made the plays when they had to.
"I'm very proud of our team. We have some things to clean up."