Cooper Flagg delivered a stupendous performance and helped the Dallas Mavericks to their first win of the season. The former Duke star delivered a sensational all-around performance, powering Dallas to a 139-129 victory over the Toronto Raptors on Sunday. Dallas rookie's mother, Kelly Flagg, was also amped after watching her son's dazzling display at the American Airlines Center.The No. 1 pick had several highlight-reel plays during the game, none bigger than the first poster dunk of his career. With just over three minutes remaining in the third quarter, Flagg received a go-ahead pass from D'Angelo Russell in transition. The rookie went full steam toward the rim and rose high to paint a vicious poster on the Raptors' big man Sandro Mamukelashvili.The crowd inside the arena went berserk and Flagg, who was fouled in the process, received a hyped-up chest bump from Anthony Davis. Flagg's mother, Kelly Flagg, dropped a heartfelt two-word reaction soon after the video of her son's viral poster dunk went viral on the internet."Yes ma’am!" she tweeted.Cooper Flagg played 29 minutes on the night and was efficient throughout the course of the game. He finished with 22 points on 8 of 14 shooting, including 2 of 6 from beyond the arc. The rookie also tallied four rebounds, four assists and one block.Cooper Flagg receives huge praise from D'Angelo RussellCooper Flagg’s electrifying dunk left not only the fans but even his Dallas Mavericks teammates in awe. Anthony Davis' instant reaction spoke volumes, while D'Angelo Russell spoke highly about the Mavericks' prodigy and commended the rookie for setting the tone for the rest of the team."He’s unbelievable," Russell said of Flagg's dunk. "He does a little bit of everything, so when he’s getting the crowd going like that, our team feeds off of it. Everybody wants to see him do great, so when he’s performing like that it’s contagious."The biggest positive for Dallas was Flagg’s explosive performance on Sunday, which helped them snap their winless streak this season. It will be a quick turnaround for the Mavericks as Flagg and Co. are slated to face the defending champion OKC Thunder on the second night of a back-to-back on Monday.