Alex de Minaur looked like a broken man when he blew a big lead over Lorenzo Musetti in his second round-robin match of the week at the ATP Finals. The Australian dropped the last four games in a row to lose 7-5 3-6 7-5, and suggested those types of losses were “eating him alive”.

But the dejected world No. 7 turned things around in less than 48 hours and played one of his best matches to beat Taylor Fritz 7-6(3) 6-3 on Thursday, ultimately earning a place in the semi-finals. And De Minaur has now credited his fiancee, British tennis star Katie Boulter, for helping him get out of a “very dark place”.

Following his defeat to Musetti on Tuesday night, a gutted De Minaur said: “I think it’s probably a good thing I don’t express my feelings right now because they’re quite dark.”

It wasn’t the first time the Aussie had lost an important match at one of the biggest tournaments, and he admitted: “I don’t know how many times I can deal with a loss like this one.”

Luckily for De Minaur, he didn’t have to deal with another defeat like that. The No. 7 seed went from agony to ecstasy as he defeated last year’s runner-up Fritz in his third and final group stage match, hitting 24 winners and winning 83 per cent of points on his first serve.

“I mean, sport…” he said with a smile after the match. “Couple days ago was one of the toughest days I’ve had in my career. I was in a very, very dark spot. I could tell you that I hated the sport. Here we are two days later and I’m feeling great about myself. It’s incredible.”

It was arguably one of De Minaur’s best performances of the year, and he credited his loved ones for pulling him out of a tough spot after the loss to Musetti.

This year’s Washington champion added: “To be honest, I’m incredibly lucky with the support system that I have, the people I’ve got around me, every single one in my team, even Katie. They were able to, or they tried to, talk some sense into me and get me out of a very dark place.

“Sometimes when you’re in that dark place, you make peace. You start to care less, right? Ultimately you can focus on other elements and not the results. For the first time in a long time, I forgot about the what if’s, the results, what happens if I miss this shot, what happens if I lose this match.

“I just committed to the way I wanted to play from the first point to the last. A couple days ago, I didn’t. That’s what hurt so much. Today I knew that no matter what, I wanted to be proud of my decision making, my aggressive mindset, and I wanted to go out there and try to win the match.”

This is De Minaur’s second appearance at the ATP Finals – and the first time he’s qualified for the semi-finals. The 26-year-old will now attempt to reverse his one-sided 0-12 record against Jannik Sinner when they meet on Saturday.