Ruiz allowed two hits and a walk in a scoreless ninth inning against the Nationals to pick up his first save of the season. He struck out two.
Ruiz had his contract selected from Triple-A Lehigh Valley on Friday.
The Phillies reassigned Ruiz to minor-league camp Sunday.
Ruiz agreed to a minor-league contract with the Phillies on Monday.
Ruiz elected to become a free agent Thursday.
The Diamondbacks designated Ruiz for assignment on Tuesday.
Ruiz did not factor into the decision Sunday, allowing three runs on five hits over 1.2 innings against the Reds. He struck out one.
Ruiz will serve as the Diamondbacks' opener Sunday at Cincinnati, Jody Jackson of Bally Sports Arizona reports.
Ruiz (1-1) was tagged with Wednesday's extra-inning loss to the Phillies. He allowed three runs (two earned) on three hits and three walks while striking out one over one-plus innings.
Ruiz allowed four runs (three earned) on three hits and one walk over one inning in Thursday's 6-2 loss to the Giants.