BOSTON -- For the Red Sox, such an electric homestand deserved a grand finale.

But nobody could have guessed the one that unfolded, which explains the euphoric reaction that took place when Franchy Cordero crossed home plate following a walk-off grand slam on an 0-2 pitch with two outs in the bottom of the 10th inning that gave Boston a wild 8-4 victory and a four-game sweep over the Mariners.

It was the completion of a 6-1 homestand for the Sox, who have won five in a row and nine of their last 12.

Cordero, a once-promising prospect for the Padres, had seen his stock drop so much that the Red Sox designated him for assignment one day before they were eliminated from the American League Championship Series last October.

Twenty-nine other teams could have claimed him. On this memorable Sunday afternoon at Fenway Park, the Red Sox had to be grateful nobody did.

At 27 years old, it isn’t too late for Cordero to reach some of that promise that sits within his impressive kit of tools.

A day after he hammered a triple to jump-start a winning rally, Cordero this time walloped a slider from Andrés Munóz over the visiting bullpen and into the first row or two of the bleachers, setting off a mob scene of white jerseys at home plate following his first career grand slam.

“Yeah, super excited to see the boys jumping around and excited and happy. I’m super happy for this moment,” Cordero said.

As well he should be. A barrage of injuries in San Diego prevented Cordero from being the player he wanted to be, and he barely even had time to unpack his suitcase after being traded to Kansas City before the Red Sox got him in the trade that sent Andrew Benintendi to the Royals.

Cordero was outrighted after nobody claimed him last October, meaning he was no longer on the 40-man roster for the Red Sox. But he was a non-roster invite during Spring Training, giving the club a chance to see some of his improvements up close.

Most notably, Cordero was in better shape and made strides in making more frequent contact.

“I told you, he’s going to start hitting the ball in the air and good things are going to happen,” said Red Sox manager Alex Cora.

When you have Cordero’s power and you can put bat to ball, good things can absolutely happen. And the outfielder, who was promoted from Triple-A on April 29, couldn’t have picked a better time for his first home run of the season.

Despite being a supporting-cast member, Cordero has made life more fun for the Red Sox. Last year, he started the dugout wave which players would do when they reached base, particularly after an extra-base hit.

This season, he has added some new gimmicks.

“[Cordero]’s quiet in the clubhouse, but then on the field, whether he’s doing the waving or breaking the bad spirits and stuff like that, that helps,” said Red Sox righty Nathan Eovaldi, who bounced back from giving up five homers in one inning in his last start to striking out a career-high 11 and allowing two runs in 6 2/3 innings on Sunday. “He’s had quality at-bats, whether it’s been walks or he’s getting big hits. Everyone is a fan of his.”

The Red Sox had endured five walk-off losses this season and gone 0-6 in extra innings this season before reversing those trends in Sunday’s thriller.

As Cordero’s drive -- which Statcast projected had an exit velocity of 106.1 mph and an estimated distance of 419 feet -- landed, there was mayhem at Fenway.

Kiké Hernández, who had delivered the game-tying single in the 10th inning, raised his right arm in triumph as he headed home. Chief baseball officer Chaim Bloom pumped his left fist and shouted something joyful from his seat in the front office suite.

Christian Arroyo dumped a huge cooler of liquid which was aimed at Cordero but instead got more of NESN sideline reporter Jahmai Webster.

“Did you see how I reacted? I was going nuts,” said Arroyo. “Last year when Franchy got over here, he became really easy to root for. He’s a great teammate. He’s got a lot of tools, and you see it right there. He could leave the yard at any point. You saw it yesterday, he hits a 111-mph triple. He’s a special talent, so to see him get up there in that situation and just relax, not try to do too much and allow the hands to kind of work and get a slider up and walk it off, that was huge, and that was a huge homestand for us.”