Alcantara, 23, has been absolutely dominant for Triple-A Nashville following his July promotion from the Double-A level, pitching to a 1.18 ERA across eight starts, with six earned runs allowed in 45 2/3 innings. He has 32 strikeouts in that span, next to just three walks.
Alcantara landed in Oakland's organization with outfielder Josh Reddick as part of the 2011 trade that sent reliever Andrew Bailey and outfielder Ryan Sweeney to Boston. He appeared to be on the fast track to the big leagues before he was slowed by Tommy John surgery in 2014.
Alcantara returned to make 15 starts for Class A Advanced Stockton in 2015, posting a 3.88 ERA to put himself back on the map.
"He's created this opportunity for himself, worked very hard from some injuries that he's had to battle through and put himself in a position to where it's his time," A's manager Bob Melvin said. "We're excited about watching him tomorrow."
The 24-year-old Cotton, meanwhile, came over in the deal that sent Rich Hill and Reddick to the Dodgers last month. He's wasted no time adjusting, stringing together a 2.82 ERA in six starts for Triple-A Nashville.
"He hasn't done anything to suggest he's not ready to pitch here, based on what our guys have seen in development," Melvin said.
Both pitchers are likely to remain in Oakland's rotation through the end of the season, given the club's lengthy list of injured arms.
Jane Lee has covered the A's for MLB.com since 2010. Follow her on Twitter @JaneMLB.