"Getting to be a part of it is way bigger than this, but this is definitely a really nice gesture," Jaso said. "He really didn't have to. I was really just happy with being behind the plate. He came through."
Hernandez inscribed "Perfect Game" on the watch, along with the date -- "8/15/12" -- it was achieved against the Rays.
"It's pretty heavy. It's got to be real," Jaso joked. "The watch I own, I think it's a Timex, so this is a bit of an upgrade."
It was just a couple of hours earlier when Jaso pondered what the gift could be, ultimately left without a clue and telling reporters, "Maybe a fastball in the back?"
"I would definitely take this over that," he later said, smiling.
Jaso was traded in the offseason to the A's as part of a three-way swap that brought Michael Morse to Seattle from the Nationals. He hit second in the A's lineup on Monday in the second Opening Day start of his career, having also started the opener for the Rays in 2011.
Jane Lee is a reporter for MLB.com. Read her blog, Major Lee-ague, and follow her on Twitter @JaneMLB. This story was not subject to the approval of Major League Baseball or its clubs.