Tuesday's announcement that third-round selection Jordy Mercer, a shortstop out of Oklahoma State University, had come to terms with the organization makes Mercer the highest of the club's picks to sign.
Shortstop Chase D'Arnaud, a fourth-round pick, and Albert Fagan, a right-hander taken in the 39th round, complete the most recent wave of signees.
Mercer and D'Arnaud have been assigned to short-season State College, which opened its season on Tuesday. They are two of four top-10 picks from this year's Draft class who already have joined the Spikes. Jeremy Farrell (eighth round, third baseman) and Matthew Hague (ninth round, third baseman) are the other two.
In all, State College will begin its season with 15 of its 30 players having been drafted earlier this month.
Mercer joins the Pittsburgh organization after being named an All-Conference player in the Big 12 in each of his three seasons with the Cowboys. Scouting reports on Mercer have him pegged as above-average defensively in the middle infield and with some pop in his bat. He hit .330 with 14 home runs and 60 RBIs this season.
Mercer also appeared in 16 games as a reliever in 2008 and ended his career at Oklahoma State with a school-record 17 saves.
D'Arnaud comes out of Pepperdine University, where he hit .314 with 11 homers and 50 RBIs in his junior season. He was selected as a First-Team member for the West Coast Conference this season.
The right-handed Fagan was a three-time Westchester Conference selection in high school before going on to pitch at Rockland Community College, where he was named the Region 15 Junior College Pitcher of the Year in '06.
While the Pirates locked down both Mercer and D'Arnaud early, there aren't expectations of doing so with either of their two earlier selections -- third baseman Pedro Alvarez (No. 3 overall) and right-hander Tanner Scheppers (second round).
Negotiations with agent Scott Boras, who represents Alvarez, are likely to continue well up to the Aug. 15 signing deadline. And with Scheppers still unable to pitch because of a frayed labrum and slightly torn rotator cuff, the Pirates will keep an eye on how the injury heals before getting deep into negotiations.
Jenifer Langosch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.