CHICAGO — Rusney Castillo can’t pinpoint exactly when he started to feel comfortable as a major league hitter.

He provided more proof Monday that, thanks to increased playing time while splitting time with fellow right fielder Jackie Bradley, Jr., he doesn’t lack confidence at the plate.

Castillo homered and drove in a careerhigh five runs, Joe Kelly won his fifth straight outing and the Boston Red Sox beat the Chicago White Sox 5-4.

“I feel like I’m finally getting into a rhythm,” Castillo said through an interpreter.

Castillo went 3 for 4 and finished a triple shy of the cycle. His sixth-inning double to the right-center field gap drove in two runs and extended Boston’s lead to 5-1.

That’s all the room Kelly and the Red Sox needed.

Kelly (7-6) allowed five hits and two runs over 7 1/3 innings – his longest outing since 2014 – while walking one and striking out three. He became the first Red Sox pitcher since Clay Buchholz in 2013 to win five straight starts.

Castillo’s three-run homer in the second gave the Red Sox an early lead and provided Kelly some ease in registering his fifth straight win.

“Those three runs and a little two-run cushion always (make) you a little more relaxed out there,” Kelly said.

Jean Machi pitched the ninth for his second save in two opportunities.

Jeff Samardzija (8-10) dropped a careerworst fifth straight decision. After giving up Castillo’s two-run double, Samardzija allowed the next two hitters to reach before being pulled after surrendering his second walk.

Samardzija struck out seven and allowed five earned runs and eight hits, including the costly ones by Castillo.

“He got me today,” Samardzija said. “It was unfortunate.

“I felt good. I thought I had good stuff today. Just a homer and a double.”

The White Sox, who had won three of their last four, cut the deficit to 5-2 in the sixth on Melky Cabrera’s RBI groundout.

The Red Sox took a 3-1 lead in the second inning when Castillo drove Samardzija’s slider over the center-field fence. The twoout blast came two batters after Samardzija drilled Hanley Ramirez in the back after quickly retiring the first two batters.

Brock Holt followed with a single before Castillo’s homer, which extended his hitting streak to nine games.

“The guy has been dynamite,” Red Sox interim manager Torey Lovullo said. “He has responded to a lot of the challenges. I know that he’s been coming on as of late and letting his game speak for itself. There is an ease and a rhythm to him.”

Chicago jumped out to a 1-0 lead on Jose Abreu’s solo homer, his 24th.