Valdez allowed both runs on solo homers and struck out eight.
Venezuela will take on Mexico in the first game Friday, while the Dominican Republic will square off against Puerto Rico in the nightcap. Two semifinal games are scheduled for Saturday with a championship final on tap for Sunday.
Cuba dropped to 1-3 with the loss and will need help to qualify for the semifinals.
"Things worked out well," said Valdez, who pitched in the Major Leagues for Arizona in 2010. "I was trying to work down in the strike zone, and thank God things worked out the way I hoped."
Balbino Fuenmayor provided much of the offense for Venezuela, hitting a home run and driving in two runs. He finished 3-for-4.
Venezuela racked up 10 hits and was 5-for-6 with runners in scoring position.
"[Valdez] gave us the opportunity to give our bullpen a rest," Venezuela manager Omar Lopez said. "Balbino had the chance to hit his first home run of the series. We also had good pitching, defense and at-bats."
Alexander Malleta and Luis Valdes each hit a home run for Cuba.
Jesse Sanchez is a national reporter for MLB.com. Follow him on Twitter @JesseSanchezMLB. This story was not subject to the approval of Major League Baseball or its clubs.