Hahn did his part with six innings of two-run ball, the damage done by Alcantara too much to overcome.
"He just got hit hard," A's manager Bob Melvin said. "It looked like he threw some good changeups, some good splits, and then it just kind of went away from him a little bit, and he centered some fastballs and they hit him."
Alcantara's season debut was greatly marred by Nomar Mazara's grand slam in a five-run second inning that also included two walks and a hit batter. It was the second home run yielded by Alcantara, who also offered up a sky-high, two-run shot to Rougned Odor in the first.
"In the first inning everything was coming out right, and I felt like I was making my pitches, but then in the second inning things kind of got away from me," Alcantara said through team interpreter Juan Dorado. "My sinker was running a little bit too far away and too up."
Hahn also had trouble with Mazara, who connected for an RBI single in the sixth and another base hit in the eighth, but the righty was otherwise effective, and his work prevented the A's from dipping even further into their bullpen.
"That was huge," Melvin said. "Just to get our bullpen kind of back in order. The last thing you want to do in a game you're down 8-0 right away is have to go to multiple guys in the bullpen. Saved us."
Less than two weeks ago, Hahn was demoted to the Minors, denied a spot on the A's Opening Day roster a second consecutive year as they opted for a rotation rounded out by Alcantara, who is out of options, and Andrew Triggs.
Hahn said Friday's outing "almost felt like a start." His efforts could potentially prompt the A's to rethink their rotation.
"Knowing we were down," Hahn said, "I just wanted to give us a shot to get back in the game, so I went out there and tried to pitch off my fastball."
"He went out there in attack mode, knew he was probably going to be out there for a while and made the most of it," Melvin said.