OAKLAND -- After scuffling greatly in his last two outings, A's starter Jesse Hahn spoke of seeking answers for the sudden dip in production -- a process that will have to take place at Triple-A Nashville, where he was optioned Sunday morning in a move that surprised the right-hander.
Zach Neal was brought aboard to take his roster spot and join Oakland's bullpen as a long-relief option.
"They told me they had to send me down because they have guys up here now they want to see make more starts," Hahn said. "It's a little frustrating. I thought I'd been having a really good season up until these last two starts. I don't want to say it's unfair because I understand it's a business thing. But I don't like that I was kind of judged off two starts there."
Hahn held himself accountable Wednesday after the latest drubbing by the Astros, who knocked him from the game in the second inning in back-to-back starts. Hahn allowed a combined 16 runs (15 earned) in four innings over that span, with his ERA ballooning from 3.56 to 5.30.
In the meantime, the A's promoted right-hander Paul Blackburn from Nashville for a start against the Braves in place of Jharel Cotton (blister) on Saturday, and Blackburn delivered six strong innings with one unearned run allowed in his big league debut.

Cotton will return to the mound Monday, while Blackburn will make his next start Thursday in Seattle.
"We wanted to take another look at Blackburn," A's manager Bob Melvin said. "He pitched really well, and Jesse has struggled a bit here recently. Finding consistency is going to be key for him. We've seen him really good, and we've seen him have some tough outings, but I think it was more about getting another chance to see Blackburn pitch."
Hahn was one of the more consistent starters before his recent struggles, giving the A's at least six innings in six of his 11 starts that preceded his June 22 outing against Houston. He yielded one home run in 59 2/3 innings in that stretch, before yielding three in four innings against the Astros.
"For me, it's just feeling good," Hahn said. "Taking a step back and getting my body right again and making sure I'm 100 percent healthy. I think maybe these last couple starts, my stuff hasn't been as good. The ball's been up in the zone a bit, and I think I've been behind in the count. So I have to do a better job managing the damage when I don't feel good in terms of throwing strikes and getting ahead of hitters, putting guys away when I have two strikes on them."
Said Melvin: "I think you go through the course of the season where you're not going to feel as good as you do on your best days. It's finding the adjustments to make when you're not feeling great to have some success. No doubt in my mind that [Hahn] will be back at some point."
Worth noting
• Melvin expressed hope that shortstop Marcus Semien (right wrist surgery) will be able to return to the A's before the All-Star break. Semien played nine innings at shortstop for Nashville on Saturday, going 2-for-5.
• Third baseman Matt Chapman (left knee infection) got four at-bats at DH in his first rehab game with Class A Advanced Stockton on Saturday and was expected to play in the field Sunday, after which the A's will make a decision on his readiness to rejoin the team.