After smashing solo homers in the fourth and fifth, Betts went deep for a third straight at-bat in the seventh, a majestic shot to left-center. All three homers were against Royals lefty starter Danny Duffy.
"I know what I can do and I know I have the ability to drive the ball, and I'm kind of showing it," Betts said. "I think it's more surprising, kind of, to everybody else. Some of it is surprising to myself, like the last one today, but I know I can drive it. It's just a matter of using the whole field and driving it everywhere."
Drew Pomeranz rode the big performance by Betts to his first win in three starts since returning from the disabled list. The lefty showed improved velocity and a better curveball than the last two times out, allowing three runs over six innings, but none after the second.
"It was pretty cool," Pomeranz said. "I'm just trying to shut them down long enough to let Mookie get at-bats. When he gets hot like that, we're all cheering for more at-bats for him. They keep throwing him pitches, but he's sitting on everything they threw at him. It's pretty awesome to watch."
It wasn't so awesome for Duffy and the Royals. The third homer by Betts was an outside fastball on the upper part of the zone that he somehow turned on to put it over the wall in center.
"The third one, that's just him being a great hitter," Duffy said.
Joe Kelly returned from his six-game suspension and pitched a scoreless seventh.
Closer Craig Kimbrel rebounded from his first blown save on Tuesday night to finish off this one, and end the homestand on a strong note for the Red Sox.
"Outstanding," manager Alex Cora said. "You've got [Alex Gordon] and [Mike Moustakas], that's a tough 1-2-3 right there, the guys he was facing. He did an outstanding job with the fastball up in the zone, being able to expand with the slider. The last pitch after a fastball up, he went back at it, and his velocity looked like it was up, so that's a good sign for him."
The homers by Betts were all solo shots. The right fielder, who was out of the lineup the previous three games with tightness in his right hamstring, went 4-for-4.
With the fourth three-homer game of his career, Betts passed Ted Williams for the most in Red Sox history. Betts ripped three homers against the Angels just 15 days ago. He joins Albert Pujols as the only active players to have four three-homer games.
J.D. Martinez also had an important homer -- a two-run shot in the third that tied it at 3.
MOMENT THAT MATTERED When Pomeranz finished his outing with a strikeout looking of Alcides Escobar, it was with a 92.3-mph fastball, the best radar reading he's had on any pitch this season. Given that Pomeranz's diminished velocity was a talking point after his first two starts, it was noteworthy that he was able to dial it up when he needed to in this start. Pomeranz averaged 89.1-mph with his fastball on Wednesday.
"We put in a lot of work between this last start and now. I threw a lot," Pomeranz said. "I watched a lot of video, did a lot of things trying to find some rhythm out there. For whatever reason, it wasn't clicking the first couple of innings. Then all of a sudden, I just kind of got it. I just kept trying to repeat it and before I knew it, we got to the sixth inning."
SOUND SMART Betts became the 17th player since 1909 with as many as four three-homer games. He is the first to have four before his 26th birthday. When Betts homers this season, the Red Sox are 13-0, and they are 31-3 the last 34 games in which he's gone deep.
HE SAID IT "It's pretty cool. He hit .400 one year. He did a whole bunch of other things I haven't done. Just to know my name is amongst his is pretty cool." -- Betts, on passing Williams for the team record of three-homer games
MITEL REPLAY OF THE DAY Down by just a run, the Royals thought they had a baserunner with one out in the ninth against Kimbrel when Lucas Duda ran to first after swinging at strike three as the ball went to the backstop. But as the Red Sox correctly pointed out, the pitch hit Duda's foot, meaning it was a dead ball. The replay official agreed as the call was overturned and Duda headed back to the dugout with a strikeout.
UP NEXT Left-hander David Price will try to get the Red Sox off to a good start to a 10-game road trip at 8:05 p.m. ET on Thursday in the opener of a four-game set at Globe Life Park. Mike Minor will start for the Rangers. Price labored in his last start, giving up eight hits, six runs (five earned) and four walks in a loss to the Rays.