Saito was signed as a free agent during the offseason and the D-backs knew the 42-year-old was a health risk, given how much time he missed last year while pitching for the Brewers.
The D-backs thought Saito was going to be healthy to start the season, but a calf injury he sustained in the final week of Spring Training forced him to start the year on the disabled list.
Saito had setbacks with the calf and then had some shoulder trouble and missed almost a month of rehab time due to illness.
Finally on Saturday, Saito made his first big league appearance the season.
"I'm really glad to be back and contributing to the team," Saito said through an interpreter before Monday's opener against the Rockies. "I just want to take one day at a time, and hopefully contribute to the team getting back to the playoffs."
Saito allowed one hit and walked one while allowing an unearned run in his one inning appearance.
"My arm felt good, my stuff felt good," Saito said. "Maybe too much adrenaline and the ball was up a little bit, but I felt good."