The 25-year-old who had to come through pre-qualifying to reach his first main draw, and almost retired this year, has a credit card debt and a room, still, in his parents' home. "Living the dream," Marcus Willis jokes, wryly. Except that, for the moment, he truly is.

Willis is the story of Wimbledon, already, for if there is a better one it is hard to imagine what that might be. The world No.772 will on Wednesday play 17-time major winner Roger Federer on centre court, where he hopes to scrounge some tickets for the singing, headband-wearing, shoe-waving, ecstatic group of tennis-playing mates who on Monday urged him to victory against world No.54 Ricardas Berankis on a raucous court 17.

Asked if he had met Federer, Willis joked that no, he hadn't seen him at the last Futures tournament in Tunisia. Asked about playing Federer, he smiled: "I'm not sure he can play on grass. That's good." Asked to compare himself with the Swiss: "Just a little bit better than me? I didn't think I'd be answering these questions in a million years."

Federer, too, is enchanted by the tale, which he describes as one of the best in tennis for a long time. "This is the kind of story we need in our sport. I think it's a great, great story. I'm very excited to be playing him actually.  It's not something that I get to do very often."

As Willis held court, almost in disbelief in the main interview room at the All England Club, he ran through what a typical working Monday back in Wokingham would normally involve. "Mini Reds four to five. Then a 14‑year‑old boy, got on the rating tour, 10 points, loving it. Then I think I got Ben Cleary six to seven. I need to look at my diary. I keep getting new lessons every now and again."

He will continue coaching, says Willis, even as the events of the past week have reinforced his determination to reach the top 100. "It's quite a nice life, isn't it, really? I haven't experienced this." His idol, Goran Ivanisevic had just come past to shake his hand. So surreal. All of it.

As recently as the start of the year, Willis was struggling to get out of bed, considering quitting the game. There was a coaching opportunity in Philadelphia. "Don't know if I would have gone or not. But yeah, I met the girl. She told me not to, so I didn't. Do what I'm told."

The "girl" is his partner Jenny Bate, a dentist, who only made it to the All England Club when the suction equipment at her dental surgery broke down and appointments had to be cancelled. Truly. Afterwards, the pair embraced and declared their love, as the crowd went nuts and security needed to escort Willis through the throng to the locker-room. A throng that, a week ago, would not have known his name.

A talented junior, but he was so wayward and undisciplined that he was sent home in disgrace before contesting the junior event at the 2008 Australian Open. He was so overweight during one Challenger  tournament in the US that the locals dubbed him "Cartman", after the rotund lad in the cartoon series South Park. Acknowledging he still has kilograms to shed, Willis says it was only three years ago that he understood the hard work that would be needed to succeed. The drive he lacked was found, at last.

"I was a bit of a loser. I was overweight," he said, admitting to too much beer and partying, some bad decisions. "I was just a loser.  I don't know. I just looked myself in the mirror, I said, 'You're better than this'."

He has already come further than anyone to reach the Wimbledon second round. So lowly ranked that he was the last  direct acceptance into pre-qualifying, and even then only when a fellow Brit had to withdraw after failing to make it back from Turkey in time, Willis then had to win another three matches at Roehampton just to reach this stage. Even now, he quips that he checks out of his hotel each morning. "I mean, I'm not a heavy favourite for any match I've been playing, so..."

But, still, on he goes, despite having never before played a main-draw match at tour-level, nor anyone ranked even as high as Berankis, having only peaked at No.332 himself. Willis is the lowest-ranked qualifier to reach the second round at a major in 28 years, having been the second lowest-ranked man to qualify for the singles main draw at a grand slam since 1998.

"It's gotten a little bit out of hand," he said, self-deprecatingly, insisting that this sort of thing doesn't happen. It just doesn't. Except that it has. "Obviously it's an amazing dream come true... I'm going to go out there and try to win the tennis match. I probably won't. I might not. But I'm going to give everything, as I have the last seven matches."

Then off he went to check back into his hotel, eat a dinner of tomato and pepper pasta with extra chicken, because that's what has worked so far. Willis has not seen the film, Wimbledon, a romantic comedy about a washed-up loser who gets the girl and wins the title. No need, though. So far, this script is better.

New material, too, for Federer, who has played the young, the poor, and the obscure, but never an opponent quite like this one. "This match is different. It's picked up on momentum. People will hear about it. People will know about it," said the seven-time Wimbledon champion. "Naturally they're going to support him. Rightfully so, because I think it's a very cool story myself."