Gail Brodsky is looking fierce on a practice court at the US Open, sending one blistering backhand after another past her opponent.

The last time the former Brooklynite played on these hallowed courts was in 2012 — after which the 21-year-old “phenom” abruptly retired from the game.

But never discount a New Yorker.

After six years and thousands of miles from the Queens stadium’s harsh lights, Brodsky is mounting a comeback. Now 27, she’s jockeying for a spot at her favorite tournament, where she first competed as a 17-year-old in 2008.

She grew up in Brighton Beach by way of Ukraine, an only child whose parents, neither of them tennis players, saw her ability early, and pushed her to become a star. Soon she was playing — and defeating — Sloane Stephens, CoCo Vandeweghe and others, making a name for herself as a promising juniors player.

But then, after five punishing years on the pro circuit, with as many disappointments as there were highs, she called it quits — after an epiphany during the middle of a US Open match.

“I thought to myself, ‘I can’t do this anymore. I’d rather be doing anything else,’” recalls Brodsky, who nevertheless finished the match for a straight-set loss. “I was done playing, and I needed to make a change.”

Twenty minutes after she stepped off the hard court, she called a coach friend, Mark Hanson, who lived outside Seattle. A few days later, she was on a plane to Washington, where Hanson signed her up as an instructor for his elite training school.

“I had spent my entire life coached by people and being told, ‘You’re not good enough,’” Brodsky tells The Post. “I grew up with a lot of pressure and not a lot of passion for the sport. [Now] I’m coaching young [kids] … who look at me like a goddess.”

She was handed a racket at age 6 and home-schooled by 13. It was a brutal schedule she endured for years, with practice starting each morning at 5:30. Her parents and coaches not only dictated when and how long she’d play, but what she could and couldn’t eat. She still can’t stomach the sight of oatmeal, something she was forced to eat as a child. It was only after she broke with her parents, at age 17, that she tasted her first French fry. (She hasn’t spoken to them since, saying only that “it wasn’t a healthy situation.”)

In 2014, she and Hanson, now 47, married. Now living in Washington, they have two children — 3-year-old Grayson and 2-year-old Brooklyn, both of whom are already taking lessons.

But even as Brodsky coached others, her relationship with the sport that she was force-fed as a child was fraught. “I was in a dark place with tennis,” she says. “I never thought I’d play tennis again professionally.” She couldn’t even bear to watch pro tennis on TV.

After years of neglecting her body, her weight approached 200 pounds. “When your body is used to being active and you stop, things can change,” concedes Brodsky, who says the 50 pounds she gained during her pregnancies didn’t help. “I was coaching a lot, but I wasn’t watching my food or working out,” she says.

During her tournament days, having an ice cream was a non-issue. But now, overeating took its toll. “I wasn’t trying to stay in shape,” she says.

That is until last year’s US Open women’s final. Although she had avoided watching tennis for years, Brodsky found herself glued to the high-drama rallying of her former rivals, Sloane Stephens and Madison Keys.

“I was sitting on the couch at home, overweight and out of shape,” she recalls. “Sloane had been a good friend of mine for so long, [and] she won the tournament and was holding the trophy. I was right there with these girls, [and] I didn’t want to have to live with questions. I didn’t want to have any regrets.

“I told my husband, ‘I think I should play again.’”

He agreed, and even helped her train.

The first day back on the court that September day was daunting. Out of shape and out of breath, Brodsky could barely muster more than five strokes at a stretch. “I knew it would be a long road,” she says.

But she stuck with it, spending as many as 40 hours on the court and enlisting a trainer for a six-day-a-week gym regimen.

Now a fit 140 pounds, she’s still incredulous that one spur-of-the-moment decision has changed her life.

She formally entered the tour in March, and by July won a tournament in Kentucky, raking in $60,000 — and the opportunity to play in Flushing Meadows. On Tuesday, she beat her opponent in straight sets.

Those who watched her star rise and just as swiftly disappear are cheering from the bleachers.

“She was just done,” recalls Joe Ceriello, who ran the tennis center where Brodsky trained for a year. “What stuck out was her grit and fight. She wasn’t this typical tennis player story. She had her struggles.

“Nothing was handed to her. She worked for it all. This comeback — going through two children and getting back on that court — is a true testament to that grit.”

These days, Brodsky brings more than a punishing backhand to the court. “I think I’m smarter on the court now. I have more perspective,” she says.

Her husband agrees. “Success is very different for her now,” he says.

Whatever happens at the Grand Slam, there’s no regret. “There’s no pressure now — it’s all passion,” says Brodsky, who keeps a keychain in her bag inscribed, “Your terms.”

“Playing is a lot more fun now. I don’t play because I have to. I play because I want to.”