KANSAS CITY (Interstat) — Sonny Gray struck out nine over six strong innings and Willson Contreras delivered a two-run homer in the sixth inning as the Boston Red Sox defeated the Kansas City Royals 3-1 on Monday night at Kauffman Stadium.

Gray allowed five hits and one earned run while walking none for his fifth win of the season against one loss. The right-hander retired the side in order in the first, third and fourth innings and worked out of a bases-loaded jam in the second. He is 2-0 in his past two starts after wins against Philadelphia and Detroit.

Contreras broke a scoreless tie in the sixth when he drove a 1-2 pitch from Seth Lugo deep to left-center field, scoring Mickey Gasper ahead of him. It was Contreras’ 10th home run of the season and gave Boston a 2-0 lead. The Red Sox added a run in the seventh on a sacrifice fly by Jarren Duran that scored Connor Wong, who had doubled earlier in the inning.

Kansas City answered in the bottom of the seventh. Carter Jensen walked to lead off against Gray, and Jac Caglianone followed with a double to right field that scored Jensen. Gray was replaced by Justin Slaten, who struck out Isaac Collins and got Michael Massey to ground out, then fanned Kyle Isbel to end the inning with the tying run at third base.

Aroldis Chapman pitched a scoreless ninth for his 11th save, striking out Starling Marte to begin the inning before inducing groundouts from Caglianone and Collins.

Lugo took the loss, allowing five hits and two earned runs over six innings with five strikeouts. He fell to 1-4.

Boston took the lead for good on Contreras’ homer in the sixth, capping a two-run outburst that included a leadoff single by Gasper. The Red Sox had nine hits in the game, while the Royals managed six.

Masataka Yoshida tripled for Boston in the fourth inning, his first triple of the season, but was left stranded after Monasterio struck out. Andruw Monasterio singled twice for the Red Sox. Marcelo Mayer also singled and scored a run.

For Kansas City, Caglianone went 2 for 4 with a double and an RBI. He doubled twice in the game, including an eighth-inning double that was his ninth of the season. Bobby Witt Jr. singled in the eighth and stole his 14th base, but the Royals could not rally.

Boston improved to 20-27, while Kansas City dropped to 20-28.

The game was played before an announced crowd of 15,531 and lasted 2 hours, 25 minutes.

Interstat’s game simulator had projected a final score of Boston 4, Kansas City 2. Interstat’s ELO system gave Boston a 50.60 percent probability to win. Boston was installed as a pregame favorite with a spread of minus-1.5. The total score of 4 went over the over-under line of 9.