Reliever Nick Vincent, who made four appearances since his big league debut on June 26, was optioned to Tucson. Vincent had pitched in each of the last two games.
"We felt as though, with our bullpen the way they've been used the past couple days, we needed a fresh arm," Padres manager Bud Black said. "Miles hasn't pitched the last couple days, so he's fresh. Nick had pitched two days in a row. Miles was throwing the ball well in Tuscon, so we made that call."
Vincent threw 4 2/3 innings with the Padres, yielding four runs on six hits.
Mikolas currently owns the longest active scoreless streak of any Padres hurler -- 9 1/3 innings -- dating back to his May 18 outing against the Angels.
The righty made his Major League debut on May 5 against Miami, and made 13 appearances before being sent back to Tucson on June 5. In that span, the 23-year-old threw 13 2/3 innings, yielding just five earned runs and striking out 12.
"It feels great to be back," Mikolas said. "It took me a week or two to figure things out the first time. It's the same game, slow it down, breathe. Already knowing that and being comfortable up here to a degree will help a lot."
Mikolas assumes a spot in a San Diego bullpen that has recorded the third-most strikeouts (266) of any in the Majors this season. That relief corps has been particularly strong of late -- an integral part of the Padres current five-game winning streak.
"Performance-wise, I have to go out there, throw strikes, and get outs," Mikolas said. "It is kind of exciting. Maybe I can help keep up this little streak they've got going."