Jeff Samardzija still winless in August after loss to Red Sox

Jeff Samardzija’s August slump continued Monday night at U.S. Cellular Field, thanks in large part to Red Sox rookie Rusney Castillo.

Castillo hit a three-run homer and a two-run double off Samardzija in the White Sox’s 5-4 loss.

Samardzija has a career-high five straight losses and a 9.00 ERA in August. After allowing 22 earned runs in his first three starts of the month, he had appeared to return to form by giving up one run in seven innings against the Angels last week.

But Castillo made him pay for his mistakes Monday.

“It’s not a forgiving game, and it really tests your will and how mentally strong you are,” Samardzija said. “You learn in this game to have thick skin and trust your work ethic and trust your routine.”

Samardzija hit Hanley Ramirez with a pitch and gave up a single to Brock Holt in the second before Castillo’s homer. He gave up a double to Ramirez and walked Holt in the sixth before Castillo’s double. He allowed eight hits, walked two and hit two batters in 5 2/3 innings.

“He did a good job of navigating through the lineup, but (Castillo) got him twice,” manager Robin Ventura said. “Dangerous hitter, not a lot of situations there to pitch around him or anything.”

Ventura also blamed the Sox offense, which mounted a two-run, ninth-inning rally. Avisail Garcia’s infield single and Alexei Ramirez’s fielder’s choice with two outs drove in runs, but Carlos Sanchez popped out with a runner on first.

Danks’ road woes: With his loss Sunday, left-hander John Danks dropped to 2-8 with a 6.48 ERA on the road. He is 4-3 with a 3.45 ERA at home.

“You’re not sleeping in your bed, (it’s) different ballparks and that routine is different,” Ventura said. “But part of our business is playing on the road, and you have to be able to put that out of your mind.”

Putnam hurting: Reliever Zach Putnam is sidelined with a sore right groin, suffered while warming up Saturday in Seattle. Ventura said he didn’t think it was serious.