De Minaur winces with pain of injury and ATP Finals KO

Alex de Minaur has bowed out of his maiden ATP Finals in Turin with a third loss and nothing to show for his typically valiant efforts, except a seemingly painful reminder of his troublesome hip injury.

De Minaur, needing a win to keep alive his already wafer-thin hopes of making the semi-finals of the season-ending men's championship, ended up wincing in obvious discomfort near the end of his 5-7 6-4 6-3 defeat by Taylor Fritz at the Inalpi Arena.

Any recurrence of the left-hip problem that first derailed him at Wimbledon in July is of concern with the looming prospect of de Minaur being drafted into Lleyton Hewitt's Australia team at the Davis Cup in Malaga next week where he's slated to play USA's Fritz again in the quarter-finals.

Jannik Sinner, who later breezed past Daniil Medvedev 6-3 6-4, and Fritz both booked their places in the semi-finals later on Thursday.

De Minaur's defeat followed losses to both Sinner and Medvedev on his maiden appearance at the Finals earlier this week, but as ever the 'Demon' didn't succumb without a real battle on Thursday despite an apparent flare-up of the injury that's dogged his second half of a terrific breakthrough season.

Still fighting furiously at the end of the second set, there was even a chance de Minaur could win in straight sets after a terrific attacking performance and still have a long-odds shot at making the semi-finals.

But having dropped just one point on serve in the rest of the second stanza, one absent-minded game when serving to stay in the set was then enough to allow Fritz to level at one-set apiece and ensure de Minaur was eliminated.

The knowledge of his exit may have knocked the wind out of de Minaur's sails as he was broken in the decider to go 3-1 down and then grimaced in clear pain after stretching to his right and trying to shift back to his left a couple of games later.

Still, though, he managed to conjure up the point of the match, with an incredible bit of retrieving and a running forehand lob that left Fritz incredulous.

The best of de Minaur's 27 winners still wasn't enough to stop US Open finalist Fritz running out the winner in two hours six minutes.

"I feel like he typically plays better in the team environment. I also feel like I play better in the team environment," Fritz said of their prospective Davis Cup match-up. "It's still going to be a nightmare to play him next week, too."

If de Minaur doesn't get a late call-up for Malaga, this will have been his final match of an excellent breakthrough campaign in which he won two titles, reached three grand slam quarter-finals and won 47 matches.

Later, home favourite Sinner outplayed Medvedev to stay perfect in the competition, looking every inch the hot favourite to go one better than last year when he was beaten in the final by Novak Djokovic, who's chosen not to defend his crown.

"I'm trying to find new ways to improve as a player," said the Italian, who's seeking to join Djokovic and Roger Federer as the only men to win the ATP Finals, Australian Open and US Open titles in the same year.

"I know what I have achieved during this year, so I try to step on court with a good mindset. I have beautiful people around me who support me daily, which for me is really important," added the man who's co-coached by Australian Darren Cahill.

Australia will be represented in the men's doubles semi-finals as Jordan Thompson and Max Purcell reached the last-four with a 7-6 (16-14) 6-3 win over Spain's Marcel Granollers and Argentina's Horacio Zeballos.