One of the top prospects in the Nationals’ minor league system will make his first professional appearance tonight. After spending the first portion of the season in extended spring training, right-handed pitcher A.J. Cole will start for Class A Hagerstown.

The Nationals signed Cole last summer with a $2 million signing bonus, a record for any player chosen in the fourth round. Tall and lanky, Cole throws a high-90s fastball and features a “spike” curveball that’s thrown hard like a slider but breaks down like a curve.

The Nationals started Cole in the minors in order to keep his innings count for the season down. They did the same with left-hander Robbie Ray, another high-profile 2010 high school draft pick, who was also sent to Hagerstown.

“We want to build a real good foundation for those guys,” Nationals director of player development Doug Harris said in early April. “We want to make sure we put the blocks down before we put up the pictures or the chandelier. Both guys were fantastic. We’re really excited about them. I want to be excited about them in July and August of ‘11 and ‘13 and ‘15.”

For the moment, at least, Cole will be teammates with Bryce Harper. Many experts believe Harper and Cole are the two best prospects in the Nationals’ system.