Matteo Berrettini became the first Italian to win a match at the ATP Finals with a surprise victory over Dominic Thiem.
The 23-year-old, beaten in his first two matches by Novak Djokovic and Roger Federer, won 7-6 (3) 6-3 at London's O2.
Berrettini knew he could not qualify for the semi-finals, while Austrian Thiem was already through following his wins over Djokovic and Federer.
Berrettini, seeded eighth, said: "I'm really proud of myself and for my team, my family and my friends.
"It's been an unbelievable season and I didn't expect at the beginning to be here. I hope to be back next year. I'm happy to finish with a win.
"I always have great fights with Thiem. I was able to stay mentally focused even when I lost my serve, and I played a great tie-break. I'm not feeling great physically so I'm happy with my performance."