Betts also hit a trio of long balls on April 17 against the Los Angeles Angels. He tied Red Sox legend Ted Williams after that performance, posting three home runs in a game for the third time in his career.
He passed Williams with his fourth career three-home run performance Wednesday at Fenway Park in Boston, Mass.
The Red Sox trailed the Royals 3-0 entering the fourth inning. Betts stepped up to the plate as the first batter in the bottom of the fourth inning. Royals starter Danny Duffy worked a 1-1 count against the Red Sox right fielder. Betts crushed Duffy's third offering -- an 83.9-mph changeup -- over the Green Monster in left field for a 452 foot homer.
J.D. Martinez knocked a two-run shot out of the park later in the inning, tying the score.
Betts stepped up again in the next inning, sending an 86.8-mph Duffy slider out of the park for his second homer of the day.
He tormented Duffy once again in the seventh frame, mashing a 92.9-mph two-seam fastball over the center field fence. That solo shot put the Red Sox on top 5-3. Kansas City first baseman Cheslor Cuthbert went yard in the top of the eighth frame, cutting into the Boston lead.
Red Sox closer Craig Kimbrel shut down the Royals in the ninth frame, earning his eighth save of the season.
Betts went 4-for-4 with three RBIs and three runs scored out of the leadoff sport. He now has 11 home runs and 21 RBIs on the season.