Their promoters had billed it as the biggest women’s boxing match in history. By Saturday’s end, surrounded by a deafening, capacity crowd at Madison Square Garden, Katie Taylor and Amanda Serrano had boxing observers immediately suggesting it was the fight of the year — without qualification.

Taylor successfully defended her undisputed lightweight world titles with a split-decision victory over Serrano in the first boxing match headlined by women at the Garden. That distinction was not lost on either fighter, each of whom was guaranteed at least $1 million, after weeks of buildup and promotion.

But as they entered the ring in front of an electric crowd of more than 19,000 people, Taylor and Serrano were focused on just one thing: winning.

“I had to dig deep in there. I had to produce a career-defining performance,” Taylor said after the fight. “We definitely got the best out of each other tonight, that’s for sure.”

She added, “This was absolutely a special, special moment — the best night of my career.”

The match was always going to be close. Serrano, 33, entered the ring 42-1-1, with 30 knockouts and as a champion in seven weight classes. Taylor, 35, had a 20-0 record, including six knockouts and four major lightweight titles. Before turning pro, she won an Olympic gold medal.

Their differing styles were apparent from the start: Serrano, originally from Puerto Rico and raised in Brooklyn, walked out to a compilation of Ja Rule’s “New York” and the Puerto Rican pop star Farruko’s “Pepas,” bouncing to the beat of the music. She was joined by her promoter, Jake Paul, a YouTube star and content creator turned boxer who helped bring new eyeballs to the fight under his company, Most Valuable Promotions. He wore pink sunglasses and a diamond-studded bow tie.

“I was told to enjoy every minute of it, and that’s what I did,” Serrano said after the match. “I just took it all in.”

Taylor, an Irish fighter, entered the arena in a measured pace to “Awake My Soul,” a gospel song by the Hillsong Worship. She was joined by Eddie Hearn, a longtime promoter with Matchroom Boxing, who wore a tuxedo.

“We represented our nations very, very proudly,” Taylor said. “Just seeing so many Irish flags in support was incredible.”

Serrano opened the first round with a series of jabs and gut shots, dancing her way around Taylor. But Taylor stayed grounded and methodical, and she countered in a way that showed she was not going to give up her title easily. As the rounds progressed, the fans got louder: At the end of the third round, it appeared the referee could not hear the bell.

In the first four rounds, Serrano laid the groundwork, through tough body shots and right hooks, for a soaring fifth round. A southpaw, she repeatedly rocked her opponent with combinations. They left Taylor staggering and snapping her head back. Serrano maintained that momentum into the sixth.

“Katie folds under pressure,” Serrano said. “That was the game plan: to go out and give it to her and have her feel my power.”

Taylor conceded that she “stood there a bit too long.” She added, “I think I was boxing very well in the early rounds and just got stuck.”

But in the second half of the fight, Taylor found her footing once again. In the final rounds, she rallied, landing big shots and combinations. Serrano opened the eighth round aggressively, but Taylor landed inside shots and big hooks across Serrano’s face, to the ballooning cheers of the crowd.

“I think courage and strength comes back in those moments purely from the hard work that I put in,” Taylor said. “That’s exactly why you train hard for those moments when you’re in the trenches.”

Serrano agreed: “She’s tough. She’s a warrior. She’s Irish. She was able to withstand the power and come back.”

As the 10th and final round approached, it was anyone’s fight. With two minutes on the clock, Serrano and Taylor engaged in an all-out brawl, matching each other jab for jab, hook for hook. As the bell rang, the fighters collapsed into each other’s arms, knowing they had delivered a fight to remember in a hall that has hosted some of the sport’s greats.

Two judges had Taylor as the winner, by scores of 97-93 and 96-93; one judge scored it for Serrano, 96-94. According to Compubox, Serrano had a 173-147 lead in landed punches. Serrano landed 36 percent of her power shots, Taylor 47 percent.

“I showed them a champion’s heart in there, as I always do,” Taylor said.

Serrano said she “gave it what I had.”

“It was a great fight. That’s all I wanted to do — to show that women can fight,” Serrano said. “I’m always going to perform like a champion — win, lose or draw. I’m always going to represent myself as a woman, as a champion.”

Taylor, who once pretended to be a boy to compete in Ireland, said the best part about her journey was being able to inspire the next generation. “Both myself and Amanda have broken barriers,” she said. “We’re both winners in a certain way.”

Serrano agreed.

“Me and Katie Taylor are true champions; we’re humble fighters,” she said. “I’m so excited that girls have two great role models they can look up to.”

With blood and sweat still drying, hints of a rematch began to percolate, perhaps one held in Dublin.

“We all want to see the best versus the best,” Taylor said. “A rematch would be absolutely phenomenal.”