(AP Photo/Alex Brandon)

If Tanner Roark wants to prove to the Texas Rangers just exactly what they gave up on five years ago, he did a good job hiding it Saturday morning.

On Sunday, Roark will make his first career start against the Rangers, the team that drafted him in 25th round in 2008 and traded him to the Nationals in 2010 along with another minor league right-hander in exchange for shortstop Cristian Guzman. It won’t be easy — he’ll face right-hander Yu Darvish, only one of the best pitchers on this big, green planet.

In time, Roark has made the Rangers regret the deal. In 116 big league innings since the Nationals called him up last fall, he has gone 10-4 with a 2.56 ERA. In 50 plate appearances for the Rangers, Guzman hit .152/.204/.174, and the Rangers left him off their postseason roster.

“They saw something else, and so did the Nationals,” Roark said. “It worked out for the better.”

Roark revealed no animosity toward the Rangers. He credited his Class AA pitching coach, Jeff Andrews, with helping him grow mentally as a pitcher.

“It was definitely a long time ago,” Roark said. “They got my career started, so I’m grateful for that, for sure. It’s a great organization.”

As Roark headed out to the bullpen Friday afternoon for a throwing session, he ran into old friends. When with the Rangers, where he reached Class AA, he played with first baseman Mitch Moreland, reliever Robbie Ross and left-hander Derek Holland. As coincidence, he works out with starter Joe Saunders in the offseason.

The Nationals may not be done benefitting from the trade: Ryan Tatusko, the other pitcher acquired for Guzman, has a 2.30 ERA with 41 strikeouts and 19 walks in 62 2/3 innings this season at Class AAA Syracuse.

One last pitching note: As he closed out the final two innings Friday night, Blake Treinen unveiled his new slider. Bullpen coach Matt LeCroy said Treinen had been tinkering with the pitch for several throwing sessions. He threw one to David Murphy, who popped it up for an out. He threw another to Luis Sardinas, who swung and missed for strike three. Both sliders traveled 85 mph. “Virtually unhittable,” Manager Matt Williams said.