BOSTON – Dellin Betances throws his fastball around 99 mph, give or take a click on the radar gun.

Hanley Ramirez waited for one.

“I was sitting on fastball the whole time,” Ramirez said.

Betances’ first pitch was a heater, but so far inside it was a wild pitch.

“Then he threw me breaking ball, breaking ball, breaking ball.”

Ramirez even flailed at one of the outside curveballs but with the count 3-1, waited for the pitch he wanted.

“Just say stay back and let it fly,” Ramirez said.

Indeed. Ramirez swatted a 99 mph offering down the middle for a three-run, walk-off homer to center field on a crisp 63-degree evening at Fenway Park.

The 7-5 improbable victory capped a five-run ninth inning.

“Unbelievable,” Ramirez said. “I’ve been saying the whole year we don’t give up.”

Saying it and doing it are two different matters.

But the Red Sox did it Thursday, pushing their lead in the American League East back to two games.

“For me, that’s my best baseball moment,” said Mookie Betts, who was on base when Ramirez homered. “Some other guys have been in playoffs and the World Series. I’m trying to get there.”

Betts’ single closed the score to 5-4 – a cursed one-run margin that often spells defeat for the Red Sox.

After the wild pitch to Ramirez, Betts stood on second base and pinch-runner Marco Hernandez was on third.

Betances was laboring.

“I mean, it was still 100 (mph),” Betts said, “and his curveball is at 85 mph. His stuff was there. Just (a lack of) command. He fell behind a couple of guys and we took advantage.”

Betts watched the fastball leave Betances’ hand, then saw Ramirez pounce.

“I just watched him,” Betts said. “I turned and there it went.”

Soon the celebration commenced on the Fenway turf.

“Something I can’t explain. So much joy,” Betts said. “Your Adrenalin gets going. You know what you did. Pretty much the best way to win.”

A walk-off to extend the division lead and push the Yankees to five games back.

Ramirez was a key player. So were Ortiz and Betts. And, Betts said, don’t forget the bullpen.

“Our pitchers did a great job holding them to five,” Betts said. “Our guys bore down.”

Boston starter Eduardo Rodriguez held the Yankees to two earned runs or less in his first six starts against them. He wouldn’t make it seven, allowing four runs in 21/3 innings. This in the same week that had starts by Clay Buchholz (six runs, three innings) and Drew Pomeranz (five runs, two innings).

Boston won that Buchholz start and stayed close in the Pomeranz game. The bullpen, cursed so often this season, is keeping the Red Sox in games.

And you won’t believe who came up big Thursday:

Robby Scott.

Scott, the former independent league pitcher who became an All-Star for the Portland Sea Dogs last year, pitched three scoreless innings.

It was only Scott’s second major league game. His debut was two weeks ago in Oakland (a shutout inning).

Scott retired the top of the order 1-2-3 in the sixth inning. After another 1-2-3 in the seventh, he escaped the eighth after allowing two singles and a walk.

“First time out at Fenway. Little bit different than pitching in Oakland,” Scott said. “Once I got settled in, just tried to get my team back in the dugout. There are no words to explain (the win). Extremely grateful for the opportunity. This team is something special.”

And maybe Manager John Farrell will trust Scott more.

Farrell walked through the clubhouse a half-hour after the game. Ramirez was toweling off in front of his locker. Farrell approached, shook Ramirez’s hand slapped his shoulder.

A good win but the Red Sox can hardly get comfortable. They are 8-5 in September.

The bottom of the rotation still needs to improve. The bats could be more consistent.

The AL East is waiting for a team to bolt from the pack. This might be the start of something big for Boston.