BOSTON — When you’re the defending AL champion and you have a double-digit lead in the division, it’s easy to shrug off a two-game slump.

Johnny Cueto had his worst start since coming to Kansas City, the Royals committed a pair of errors and managed just four hits against a rookie making his fourth start Friday night as they fell to the Boston Red Sox for the second straight night.

Boston Red Sox starting pitcher Henry Owens delivers a pitch in the first inning of the Red Sox’ 7-2 win Friday night in Boston. Owens pitched eight innings to earn the victory. The Associated Press

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WHO: Kansas City Royals (Ventura 7-7) at Boston Red Sox (Barnes 3-3)

WHEN: 7:10 p.m. Saturday

TELEVISION: NESN

“No aspect of our game was tremendously good tonight,” Manager Ned Yost said after the 7-2 loss. “It’s rare when it happens, but it happens.”

The Royals entered the series against last-place Boston with a 14½-game lead in the division and a five-game winning streak.

Cueto (2-2) had allowed just six runs in four previous starts for the AL Central-leading Royals. He allowed six earned runs and 13 hits Friday, striking out three before leaving after six innings. The Royals also committed two errors, leading to another run.

“He’s been doing a good job since we got him,” center fielder Lorenzo Cain said of the right-hander who was acquired from the Cincinnati Reds just before the trading deadline. “Unfortunately, I just speak for myself, I played terribly.”

Henry Owens of Boston made the longest start of his short career, pitching eight innings of four-hit ball. Blake Swihart had four hits and Mookie Betts three for the Red Sox, who tied a season high with their fourth straight win.

A 23-year-old left-hander who is one of Boston’s top pitching prospects, Owens (2-1) was making his fourth career start since being called up Aug. 4 from Triple-A Pawtucket. He pitched well in his first two outings, but gave up seven runs and 10 hits Sunday in a loss to Seattle.

Owens allowed Kansas City one earned run, and four hits and a walk, striking out four in eight innings. The Red Sox got to Cueto for three runs in the second inning, two in the fourth and two more in the sixth.

Josh Rutledge hit a two-run homer for Boston. Alcides Escobar hit a solo shot for the Royals.

Boston led 4-1 in the fourth when Betts lofted a blooper to right-center. Cain ran hard for it and when he tried to scoop it up on one hop, he swatted it away into right field. Betts took second and Swihart scored from first. The Royals also made an error in Boston’s three-run second, when Escobar just failed to field a relay throw from the outfield.

Swihart, another 23-year-old rookie, had his second career four-hit game and was in the middle of all three Boston rallies.

He doubled in a run and scored in the second; singled in a run and scored in the fourth; and singled to start the sixth-inning rally, scoring on Rutledge’s homer.

“He’s a great student of the game,” said Red Sox bench coach Torey Lovullo, who is filling in as manager while John Farrell is being treated for lymphoma.

“He pays attention, and we feel like it’s a really good sign of things to come.”

NOTES: Royals second baseman Omar Infante returned to the lineup after missing three straight games with back spasms. … Red Sox right-hander Clay Buchholz, who received a plasma-rich platelet injection in his elbow after the All-Star break, has not been cleared to resume throwing, Lovullo said. … Royals right-hander Yordano Ventura (7-7) makes his 20th start of the season Saturday night. Ventura went seven innings in his previous start, allowing two runs in a 4-3 win over the Angels in 10 innings Sunday. Red Sox right-hander Matt Barnes (3-3) is set to make his second major league start after getting rocked in his first. Barnes allowed six runs over five innings in an 8-2 loss to Cleveland on Monday.