"We've seen him in any number of roles," Melvin said. "We'll bring him in in leverage situations in the seventh. We've brought him in for last out in the eighth and the ninth. He's done a nice job for us."
Melvin has previously stated that the A's wanted to get a look at the 29-year-old in the closer's role, and though Treinen blew a save in his first crack at the ninth inning July 27, he's converted all three chances he's had since and thrown six scoreless ninth innings in a row.
"We thought all along that he had the stuff to be able to close. I know he had a tough time in Washington with it, but knock wood, he has not for us," Melvin said. "Sometimes, all you need is a change of scenery to get some of the baggage that might've been there. Right now, he fits the bill for us in that inning."
The right-hander doesn't shy away from his early season struggles, saying, "I think the biggest thing was getting a chance to be comfortable with it and learning it. It's a little bit different than throwing in situations that I had success in last year. That took some adapting.
"I wasn't getting the job done in D.C. I don't fault them for not letting me ride with it. I hate that I wasn't able to solidify that role and give them a solid presence back there to allow other guys to fall into a role that's more consistent."
But after being traded July 16 for relievers Sean Doolittle and Ryan Madson, Treinen has settled in with the organization that drafted him in 2011.
"I'm very thankful to be back in the A's organization. I'm thankful for my time in D.C., and it was a great experience. But it's a new chapter now," Treinen said. "I just want to be in a consistent role over here and give the team something to hang on to late in the game, whether it be the seventh, eighth or ninth. I just want to make sure I do my job."
• Outfielder Boog Powell made his A's debut Saturday night, batting leadoff and playing center field. Acquired Sunday in a trade with Seattle and called up Friday, Powell was in Friday night's lineup but was scratched 45 minutes before first pitch with an upper respiratory infection.
• Outfielder Jake Smolinski (right shoulder surgery) is starting a rehab assignment Saturday with Class A Advanced Stockton, where he'll be the designated hitter. Melvin added that Smolinski will only be hitting for the time being as he continues a throwing program.