Betts collected four hits and recorded the 13th multi-homer game of his career -- and third this season. It was his second three-homer game in 2018 and fourth of his career, moving past Hall of Famer Ted Williams for the team record.

The 25-year-old outfielder also became the first player to have four three-homer games in his career before age 26.

In his second game back from a brief absence caused by a hamstring injury and first game back in the starting lineup, Betts homered in the fourth, fifth and seventh innings off Royals starter Danny Duffy (0-4).

Betts became the fourth player in the American League to reach double digits in home runs and took over the major league lead with 11.

J.D. Martinez added a two-run homer for Boston, which had a three-homer game for the 31st time in team history.

Drew Pomeranz (1-1) allowed three runs and eight hits in six innings after serving up three homers in a Friday loss to the Tampa Bay Rays.

Joe Kelly struck out two in a scoreless seventh in his first appearance following his six-game suspension. Matt Barnes allowed a run in the eighth, and Craig Kimbrel struck out the side in the ninth for his eighth save in nine chances.

Salvador Perez hit a sacrifice fly, Drew Butera hit a two-run double and Cheslor Cuthbert homered for the Royals.

Duffy allowed five runs and nine hits in 6 2/3 innings. The left-hander dropped to 0-5 in his career against the Red Sox.

Duffy tied a career high by allowing three homers in a start for the eighth time and second time this season. It was the second time he allowed three homers at Fenway Park (also Aug. 27, 2016).

The Royals took a 1-0 lead on Perez's sacrifice fly in the first but missed a chance for more when center fielder Jackie Bradley Jr. threw out Jorge Soler trying to advance to second. They went up 3-0 on Butera's two-run double with two outs in the second.

Boston cut it to 3-1 when Betts opened the fourth by lifting a 1-1 changeup over the Green Monster. After Duffy walked Hanley Ramirez, Martinez tied the game by lifting a 2-1 slider into the seats atop the left-center-field fence.

Betts made it 4-3 with one out in the fifth when he drove Duffy's 0-2 slider inches inside the left field foul pole. He slugged his third homer with one out in the seventh, blasting a 1-2 fastball over the center field seats. Betts is hitting an absurd .480 this season when he is down in the count, nearly .300 points higher than the major league average.

Betts' third homer turned out to be the game-winning hit as Cuthbert made it a one-run game by tucking in a homer inside the Pesky Pole in right field. After Barnes put the tying run on, he fanned Alcides Escobar.

--Field Level Media