"He's done as well as anybody in camp," Cubs manager Dale Sveum said of the right-hander. "He's showed a lot of poise."
On Saturday against the Padres, Castillo walked two and struck out one of the five batters he faced. He has fanned 10 over 8 2/3 innings. The only glitches, Sveum said, have been Castillo's defensive work. He's also missed some signs. But the pitches and his poise have been impressive.
"For a young kid, he hasn't had any big hiccups as far as throwing the ball all over the place," Sveum said. "As soon as he throws a ball, he'll come back with a strike. He'll throw a slider for a strike when he's behind in the count."
James Russell also appears to have secured a spot, and Sveum said they may break camp with one lefty in the bullpen.
"We could go with two," Sveum said. "We could go with none -- who knows? There's no doubt we could just go with one."
He was kidding -- sort of -- about not having a lefty.
"Teams have been pretty good without one," Sveum said. "I'm sure it's not going to happen. We never really had one last year in Milwaukee when we won 96 games. That's just talking. James Russell has thrown the ball well, and I'm sure he'll be fine and on the team. There's times when you go with no lefties, when you have other guys with sinkers and guys who can get the ball moving on both sides of the plate."
The Cubs want to see more of Frankie De La Cruz, claimed off waivers from the Brewers.
"He's a very durable guy who can pitch a lot, and he's got a good changeup," Sveum said. "His thing is just throw strikes."