He allowed Ichiro Suzuki's 2,991st hit in the eighth inning, then made an errant pickoff throw that allowed Suzuki to advance to second base. He finished the night with one walk, one strikeout and an unearned run.
"I thought he looked good," manager Mike Matheny said. "Taking a long break, we had to be careful there. We kind of pushed him as far as we wanted to push him in terms of the pitch count. I thought he did a nice job when he came in."
Siegrist began feeling symptoms of weakness June 16, and the team initially thought it might be a sinus infection before finding out it was mono.
"I was a little bit surprised," Siegrist said. "I was happy to know what it actually was and not wonder about it. When they told me what it was, everything kind of made sense."
Siegrist stayed in St. Louis for the duration of his time on the DL, but rested at home, away from the club, as a precaution. He was cleared to throw last Friday and tossed two 25-pitch bullpen sessions over the past week.
"My arm actually felt really good, just every time I came out of the game, I felt just tired," he said. "[I] just wasn't really into what I was trying to do, because I was just out of it."
The team ran another set of blood tests before clearing him to pitch, and he'll continue to monitor himself to make sure he doesn't experience chronic fatigue.
Siegrist went 5-2 with a 2.78 ERA and one save in 35 relief appearances this season before going on the DL, fanning 34 batters in 32 1/3 innings. The Cardinals' bullpen roles have been in flux; Matheny does not expect to try Siegrist in a closer role, though Siegrist will add some much-needed stability.
"He's done a nice job in the role we had him in," Matheny said. "I imagine that's going to continue."
Tuivailala, 23, allowed three runs in two innings over three relief appearances from July 3-6.