In a blockbuster new book, John McEnroe reveals he “hated every minute” of his wedding to Tatum O’Neal — and the two were high on drugs the first time they made love!

What’s more, McEnroe claims his bad-boy antics on the tennis court were just “an act” to fill stadium seats!

The 43-year-old ex-tennis champ — who hosted the heartbeat-busting TV show “The Chair” — rips the lid off his private life in his upcoming autobiography “You Cannot Be Serious” . . . and The ENQUIRER has a sneak preview of all the juicy details!

McEnroe and Oscar-winning actress Tatum were only in their 20s when they hooked up.

“In the book Mac writes, ‘We were just kids, really — mature beyond our years in some ways, quite young in others,’ ” an insider disclosed.

“The first time they made love, they were high on drugs.

“It wasn’t romantic, it was just, ‘Let’s just do it, so we can say we did it, and then we’ll know we mean something to each other, and we’ll really get into it when we’re in a better frame of mind,’ Mac writes.

“The tryst took place in a room at Farrah Fawcett’s house that was ice-cold.

“Mac confides, ‘It was just awful.’ “

When Tatum told McEnroe that she was pregnant, “he was sick,” the insider revealed.

“He didn’t know if it was the rich casserole that Tatum’s mother had cooked the night before or the baby news. But he couldn’t stop retching.”

Their son Kevin was born May 23, 1986. The couple tied the knot Aug. 1, 1986.

“Mac says, ‘I hated every minute of it.’

He posed for photographers outside the church, but the occasion held no pleasure for him,” the insider revealed.

During the peak of his tennis career, McEnroe claims that he intentionally threw temper tantrums on the court.

“Mac says he was egged on by tournament officials who knew they could fill stadium seats if he played,” the insider confided.

“Mac writes: ‘It happened at tournament after tournament: I would freak out, the umpire would hit me with a warning, a point penalty, maybe a measly fine or two (in a year where I was earning a couple of million dollars, $700 was pocket change) and life (and the match) would go on. If I went home, they lost money.

” ‘The tournament directors knew it, the umpires knew it, and the linesmen knew it. I knew it.

” ‘The system let me get away with more and more, and — even though to some it looked as if I was glorying in my bad behavior — I really liked it less and less.’ “