MESA, Ariz. -- Mark it down. The A's got a keeper in left-hander Sean Manaea.
He isn't in the big league plans for Opening Day. It won't, however, be long before Manaea makes his debut.
Manager Bob Melvin heard all the hype in the aftermath of the A's acquiring Manaea last July from the Royals in exchange for second baseman Ben Zobrist. This spring, he has gotten to see Manaea in action, and seeing, in this case, is reassuring.
"This is our guy, as far as pitching prospects go," Melvin said.
Manaea made his fourth appearance of the spring against the White Sox on Sunday afternoon, and not even a Jerry Sands home run following a one-out walk to Melky Cabrera in the first could taint the picture of potential that Manaea put on display.

He worked 3 2/3 innings, and struck out seven, including Jimmy Rollins to open the game, giving him a Cactus League line of 15 strikeouts, six walks and seven hits allowed in 10 1/3 innings spread over four appearances.
Now, he's not expected to break camp with the big league team.
The A's seem pretty set on a season-opening rotation of Sonny Gray, Rich Hill, Jesse Hahn, Kendall Graveman and Chris Bassitt, with Felix Doubront as the first reinforcement.
And then comes Manaea, MLBPipeline.com's No. 2 prospect in the A's system, with a professional resume that includes only 39 Minor League starts, none higher than Double-A, where he was 6-0 with a 1.90 ERA in seven starts for Midland after his acquisition from the Royals.
But that is not a surprise. Prior to his junior year at Indiana State, Manaea was considered one of the top two prospects for the 2013 Draft. He, however, sustained a hip injury that spring and slipped to the Royals with the 34th pick.
There are no residual problems from the hip, and while he did miss the first half of the 2015 season with an abdominal strain and then a groin injury, there has been no indication of any lingering issues since he went back to work in the Minor Leagues last June.
Now, it is just about fine-tuning his pitches and awaiting his turn in the big leagues.
"Obviously, I want to make it to the big league team sometime this season and stay up," he said. "What I think about is working hard and hoping good things happen. There's nothing I can do to make the front-office guys feel different."
And Manaea knows about working hard. His dad, a native of Samoa who spent time in Hawaii, is a Vietnam veteran who was stationed in Indiana, where he stayed after getting out of the service, working in the steel mills of Gary.
Manaea played basketball until his sophomore year in high school, and baseball ever since he can remember. But the 6-foot-5, 245-pounder never even dabbled in football.
"My dad didn't want me to play football," said Manaea. "I was almost this tall in high school, but I was skinny. My focus was baseball, and I loved every second of it."
The focus is paying off.
He is a hero in his hometown of Wanatah, Ind., which had a population of 1,048 in the 2010 census, and according to Manaea, "there's only one stoplight, and there's a Subway and a Burger King."
And now there is Manaea, whom Wikipedia lists as the only person in the section of "notable residents" from Wanatah, home of the Scarecrow Festival at the end of September every year. Manaea was asked to be the grand marshal of the festival parade, but had to decline because of his baseball commitments. His parents wound up filling in for him, and there was a cardboard cutout of his head in the front of the car.
"That," he said, "was pretty cool."
And that is a lot of emotion for Manaea.
"My dad and me are pretty laid-back," he said. "We try not to worry about things, just go with the flow. It's how I live life."
The flow is carrying Manaea along at a pretty good pace in the baseball world.
It is why Melvin has worked to make Manaea very much a part of the pitching plans this spring, providing an opportunity for the big league staff to get an extended look at Manaea so it has a better feel of the scouting reports it receives while awaiting his arrival.
So far, Melvin likes what he sees, particularly on a day like Sunday, when Manaea wasn't as sharp as he has been.
"He has a fastball he can throw by people in a fastball count," said Melvin. "He struggled with his breaking ball and had some trouble with the fastball inside to right-handed hitters, but he made adjustments on the fly.
"It is very difficult for a young pitcher to make adjustments like that."
Manaea made them.
But then Manaea is not just any young pitcher.