Signed by the A's out of Venezuela as a 16-year-old for $2.2 million in 2010, Nunez was primarily groomed as a third baseman, before adding first base and left field to his now-diversified repertoire. Whether he gets playing time with the A's at any of these positions this month remains to be seen; he could get designated hitter at-bats.
"Just a reward for him being here is significant, because he deserves to be here," A's manager Bob Melvin said. "We're a little muddled as far as where those at-bats will come from. But we have to get him in there at some point in time.
"Certainly Renato is a guy who has been impactful down there at every classification he's been. We're excited about where our future's going, and to get guys up here and to get guys here and get them experience at the big league level is important."
All have since graduated to the Majors, and Nunez hopes to stick, too -- though he's at risk of leaving the organization this winter, since the A's must keep him on their 25-man roster next season or be forced to expose him to waivers.
"I'm pretty happy to be here with my friends, my teammates I've had my whole career," Nunez said. "I'm here to try to help the team win. That's what I'm here for. Keep working and try to do something to help my team win."
Mengden, meanwhile, will immediately enter the rotation, taking the spot of a struggling Chris Smith, who has been moved to the bullpen. The right-handed Mengden, who is penciled in to start the second game of Saturday's doubleheader against the Astros, made two starts with the A's during a short stint earlier this summer. He was placed on the Minor League disabled list shortly thereafter with a right oblique strain and went 0-3 with a 6.09 ERA in five starts with the Sounds following his return.
Mengden, who came to the A's in the 2015 Scott Kazmir trade with Houston, also made 14 starts for Oakland last year, pitching to a 6.50 ERA.
"One of the younger guys we got in trades, and should be significant in the future for us," Melvin said, "so we'll give him a shot."
Melvin's overworked bullpen will welcome Alcantara, who began the season in Oakland's rotation before being designated for assignment. He posted a 2.67 ERA in 18 games, including three starts with Nashville, missing two months with a right elbow strain. Right-hander Paul Blackburn (right hand contusion) was transferred to the 60-day disabled list to make room for Alcantara on the 40-man roster.
Wendle, the A's No. 23 prospect, is back for a second September with the A's, after hitting .285 with eight home runs in 118 games with Nashville.
Jane Lee has covered the A's for MLB.com since 2010. This story was not subject to the approval of Major League Baseball or its clubs.