OAKLAND -- The A's expect A.J. Puk to serve as one of the anchors to their starting rotation for years to come. His first chance to make an impact in the Majors, however, will come in a different role.

Puk, rated Oakland’s No. 2 prospect and No. 43 overall by MLB Pipeline, arrived to the Coliseum before Tuesday's series opener against the Yankees and is expected to work out of the bullpen.

• What to expect of Puk in Majors

In order to make room on the active roster, the A's optioned left-hander Wei-Chung Wang to Triple-A Las Vegas on Monday.

“You draft these guys and follow them through their Minor League careers. There’s a reason we’ve handled this guy the way we’ve handled him,” A’s manager Bob Melvin said. “He’ll be a starter down the road, but at this point, he’s been conditioned for this. Now he’s in the big leagues and the training wheels are off.”

Puk, who was selected sixth overall in the 2016 Draft by Oakland, has pitched mostly as a reliever this year. The 24-year-old southpaw has appeared in 18 Minor League games, with four starts, posting a 4.97 ERA over three levels this season. He was promoted to Triple-A on July 23, going 4-1 with a 4.91 ERA and a 0.909 WHIP in nine games for Las Vegas -- all in relief.

Converting from starter to reliever requires a switch in mentalities, something Puk had experience with in college.

“You have to be locked in every day,” Puk said. “Starting, it’s just one day, and the other days you have your routine. As a reliever, they call your name and you’re in. It gives you a nice adrenaline rush to get up and going.”

The big league debut for Puk will be a shining light at the end of what was a dark tunnel in 2018. The left-hander was on the fast track to the Majors and fighting for a potential rotation spot during a Spring Training that saw him allow no earned runs through his first three outings. But in his fourth start, Puk’s velocity decreased dramatically from the usual 96-98 mph to around 90-91. After consulting with Dr. James Andrews, Puk underwent Tommy John surgery that cost him the entire season.

From that last Cactus League game against the Mariners on March 15, 2018, Puk went through the long and grueling rehab process that comes with the elbow surgery. Over a year later, Puk made his return to game action for a start with Class A Advanced Stockton on June 11.

“My first game back in Stockton was one of the greatest days of my life,” Puk said. “It’s been a long year. A lot of hard work went into this, and now it paid off.”

Puk is expected to return to a starting role next season. He still does not possess his full complement of pitches as he’s stayed away from throwing his changeup to avoid elbow discomfort, though Puk did say he started throwing the pitch in bullpen sessions this past week. For now, his three-pitch arsenal, which features a 97-mph fastball to go along with a slider and curveball, should suit him well as he looks to provide the A's a boost in the back end of the bullpen.

“He throws rather hard. He’s got a good slider and has developed into the guy we expected him to,” Melvin said. “We’ve been excited watching his progress and excited to have him.”

Racking up 38 strikeouts over 25 1/3 innings in the Minors, Puk certainly has the power arm that is almost a necessity in big league bullpens these days to combat the home runs that are being hit at a record pace, and Melvin won’t hesitate to unleash him in a critical situation.

“I’m not afraid to use him in a big spot,” Melvin said. “Every time I’ve said a certain way we’re going to use a guy, we end up playing 14 innings and he’s in the 12th in a tie game, so we’ll see. Jake [Diekman] has been doing a nice job for us as that late lefty. A.J. is a guy we’re not afraid to put on some righties, too.”

Regardless of the spot Melvin decides to bring Puk in for his debut, he'll take the mound in front of a large crowd against the Yankees that will include his father, Dave, his mother, Chris, and his three siblings.

“I’ll probably be juiced up a lot,” Puk said. “We’ll see. I’ll try to stay relaxed and do the job.”

Garneau clears waivers

The A’s were pleasantly surprised to learn that catcher Dustin Garneau, who was designated for assignment Friday, cleared waivers and accepted an assignment to Triple-A. He’ll provide depth at a position that is thin throughout the organization.

“Dustin fits in really well here,” Melvin said. “We were happy that he could sneak through and good chance we’ll see him in September. He knows our pitchers and understands how we do things here.”