Last week in Houston, as Washington Nationals players poured out of the visitors’ dugout to celebrate a victory over the Astros, Gio Gonzalez and Doug Fister bolted ahead of their teammates, like two kids playing tag. Fister caught Gonzalez and wrapped him in a headlock. Gonzalez wanted to return the favor, but Fister stands 6 feet 8 inches. “I don’t think I can get up that high,” Gonzalez said. Since the start of spring training, when he arrived as the biggest acquisition, literally and figuratively, of the Nationals’ offseason, Fister has consciously ingratiated himself with teammates. He has played cards in the clubhouse, talked strategy in the dugout, shagged flies in batting practice. But he knows the moment he will truly become part of the Nationals will come Friday night in Oakland, Calif. Thirty-five games into the season — and three days after Robbie Ray, the pitching prospect traded to acquire Fister, earned his first win for the Detroit Tigers — Fister will make his Nationals debut. Having conquered elbow inflammation during March and rehabbed from a strained lat muscle in April, Fister will give the Nationals the rotation they imagined in the winter and will give Fister what he wanted all along. “I’m more excited to be part of the team,” Fister said. “Yes, I’ve been here. But I’m excited to help any way that I can now, get out there and get off the mound for the first time for these guys and really feel a part of the team. It’s been a long time coming. I’m pretty amped about it.” Without Fister, the Nationals’ starting rotation has been solid. Its 3.55 ERA ranks 10th, but 19 rotations have thrown more innings. Remove Taylor Jordan from the rotation, and the Nationals starters’ collective ERA would shrink to 3.24. With Fister throwing his cannonball sinkers, it should only improve.