Midway through Broadway’s “Betrayal,” Zawe Ashton has her eye on Tom Hiddleston’s melon.

The “Avengers” star plays Robert, a man who’s just discovered that his best friend, Jerry (Charlie Cox), is having an affair with his wife. The men are having a fancy but fraught dinner together as Robert, repressing his rage, hacks into his appetizer, sometimes sending some of it flying.

“We’ve seen that melon go lots of places,” says Ashton, who, as Robert’s wife, Emma, sits in the background during that scene. “One night it went under Tom’s chair, another night, it went into the audience . . . It hasn’t flown off in New York yet, but I’m looking forward to it!”

The newest revival of Harold Pinter’s 1978 play opens at the Jacobs Theatre Thursday night, after a brief, sold-out run in London. Inspired by the playwright’s affair with a married woman whose husband he befriended, this “Betrayal” has Ashton wrapping her arms and legs around her leading men for eight shows a week.

Is she the luckiest woman on Broadway or what?

“I would say that Tom and Charlie are the luckiest men on Broadway, to have such a wonderful tryst partner,” the 35-year-old tells The Post, laughing. “No, I’m joking! Honestly, the emotions in the play are so intense that that part of it isn’t really conscious.”

Over a late, pre-show lunch, the willowy (5-foot-10) Ashton proves every bit as exuberant as her first name, pronounced “Zow-ee,” sounds. She grew up around the corner from Pinter’s old home in Hackney, London, the daughter of a Ugandan mother and an English father. Gangly, frizzy-haired and bullied, she lived for the theater classes she took every weekend, from ages 6 to 20. By 11, she snared her first real gig on British TV, and has worked steadily — acting, as well as writing and producing — ever since.

It was at a gala charity fundraiser a year ago that she first teamed with Hiddleston. The two performed a scene from “Betrayal” — a particularly wrenching one, in which Robert discovers Emma’s infidelity — and the audience, which included Pinter’s widow, Lady Antonia Fraser, assumed they were about to star in a revival.

No, they weren’t, Ashton says, “but the seed was firmly planted.” Before she knew it, they were in rehearsals with Cox and director Jamie Lloyd.

“We instantly trusted each other,” she says of herself and her co-stars. “We were nicknamed ‘The Trupple’ by the crew, because we’d just go everywhere together! Every evening after rehearsal, we’d all sit down and have a cup of tea and talk. We had the best time! I think that’s often the way with difficult material — you counterbalance it with immense amounts of laughter and trust.”

She says she feels protective of Emma, a gallery owner and mother of two with a complicated love life who is, perhaps because of her unabashed sexuality, often seen as the villain of the piece.

“The first few times in London, when I left the theater, people said, ‘I hated you,’ ” Ashton says. “I actually had someone call me a whore . . . But I’ve had other people say, ‘Oh, I’ve lived through that.’ It’s funny, but the people who really understand Emma come up to me with tears in their eyes.”

Ashton, who’s managed to keep her private life private, says she’s never married, nor does she have any children. But she clearly enjoys playing someone who does.

“I feel kind of badass in this role,” she says. “Emma’s got two kids, a career and she’s having so much sex!

“To be a Pinter woman is a wonderful experience!”