These selections followed their decision to draft outfielder Billy McKinney with the No. 24 pick.
Overton was initially drafted by the Red Sox out of high school in the 26th round three years ago, ultimately deciding to go to college and join the Sooners' staff alongside Thursday's third-overall pick Jonathan Gray.
That meant Overton received plenty of exposure to scouts during his junior season, when he went 9-2 with a 2.91 ERA, striking out 76 and walking 22 in 86 2/3 innings. The 6-foot-2 southpaw, who sports a wiry frame that weighs in just over 170 pounds, would've racked up more had a left forearm strain not sidelined him for a couple of weeks.
A's scouting director Eric Kubota says the organization is "confident as to where he is medically."
"He's a guy that pitches anywhere from probably 88 to 94 [mph]," Kubota said. "He can really pitch with his fastball. He's flashed a plus breaking ball. I know he doesn't necessarily look like a power pitcher physically, but he can pitch that way at times. He's got a very good changeup. He's polished and has upside to his stuff."
Pinder, meanwhile, hit .321 with eight home runs and 50 RBIs in 60 games for the Hokies this season. He started the year at third base, then moved to shortstop midway through the season and is said to be able to play all over the infield.
For now, the A's are viewing him as a shortstop, the same position 2011 first-round pick Addison Russell plays.
"He's been mostly at third base through his career, but we were encouraged by his defense at shortstop and we do think he has a chance to stay at that position as his career progresses," Kubota said. "We have some guys on our scouting staff who really, really liked him. We saw him a lot through the spring, and we were particularly surprised he was still available because he really, really played well at the end of the season."
Pinder is the son of Chris Pinder, who was drafted by Baltimore in the seventh round in 1987 and played in the Minors with the Orioles and Indians.
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.