Reed got to the ballpark early and spent time saying hi to his former mates.
"Definitely different," he said while looking around the visitor's clubhouse. "It was weird walking in the tunnel and going past the home clubhouse. The next three games they're the enemy so I hope we come out of here with three wins."
White Sox manager Robin Ventura said his team misses Reed's reliability at the end of games.
"He always wanted the ball," Ventura said. "He always was available, he'd do anything."
Reed has converted 10 of his 11 save opportunities for the D-backs this year after saving 40 games for Chicago in 2013.
Steve Gilbert is a reporter for MLB.com. Read his blog, Inside the D-backs, and follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.