BOSTON — Mookie Betts and the Red Sox gave the Yankees and Brian Cashman a booming message Friday night at Fenway Park: You had better trade for another starting pitcher.

Betts slammed three home runs off James Paxton in his first three at-bats as the Red Sox cruised to a 10-5 victory. If you’re counting, that’s 29 runs against the Yankees in two nights and Betts is rolling with six hits in those two games.

The Yankees came here with the idea of burying the Red Sox in the AL East, but after these two slaughters, the Red Sox are gaining life in the division.

While the Yankees ponder the trade market, the Red Sox landed Andrew Cashner and he survived 6²/₃ innings, scattering 10 hits while striking out six.

This was Paxton’s first performance at Fenway and he was terrible right from the start with Betts’ leadoff home run.

Red Sox manager Alex Cora pointed out that Betts is extremely hard on himself and this was a night he needed.

“It’s always cool when he smiles on the field,’’ Cora said of last year’s AL MVP. “Tonight was one of those big nights. Hopefully this is the beginning of something great here.’’

Betts doubled in his fourth at-bat and grounded out his last at-bat. Before the game, he took the time to take a 10-year-old from the Make-A-Wish Foundation around. There was one report that the child asked him to hit a home run. Turns out, Mookie hit three.

“I’m glad he came,’’ Betts said. “He’s our good luck charm.

“It’s been a long year, obviously not the same as last year,’’ Betts said of the Red Sox’s struggles. “I’ve been putting a lot of work in behind the scenes. It was a good day.’’

Betts said the key to his at-bats is to “try to turn your brain off and just play. That’s when everybody is at their best.’’

Don’t overthink it.

Asked if the Red Sox could still be a playoff factor, Betts smiled and said: “Yes, it’s just a matter of time. Now is the time. It’s late and it’s getting later. Gotta put wins together.’’

In addition to Betts’ huge night, J.D. Martinez homered in the first innning as well. Paxton has surrendered 10 first-inning home runs over his 18 starts.

The way the Red Sox are hitting, the next thing you know they will come out with their own “Savage in the Box’’ T-shirts.

Betts is finally on a tear and this marks the third time in his career he had a three-homer game. He has reached safely in each of his past 23 games. Betts makes the Red Sox’s offense go, and they are going strong now.

In the past, the Yankees really only had to worry about one other muscular opponent in the AL and that was the Red Sox. With the Twins hitting baseballs out of the ballpark at a record pace, they have two crushing opponents (and the talented Astros as well) and facing the Twins and Red Sox back-to-back has shown how vulnerable this Yankees pitching staff is against power teams.

In his fourth at-bat, Betts doubled in a run, giving him 14 total bases and five RBI in four at-bats. No Red Sox player has ever hit four home runs at Fenway Park. Betts faced lefty Zack Britton in the eighth and grounded to third.

The Red Sox clearly were suffering from a World Series hangover, but this win put them 11 games over .500. They have the highest payroll. They are defending world champions and they are beginning to play like it. The Yankees are still way ahead in the loss column with a 10-game lead, but these two most recent losses give them a lot to think about and should make Cashman that much more aggressive on the trade front.

Betts gets the offense started for the Red Sox. In 2018 he won a world championship, a Gold Glove, a Silver Slugger and the MVP award. He can do it all. He is a special player and he is again at his best making the Red Sox one scary opponent.