American Taylor Fritz outlasted Felix Auger-Aliassime in three sets and Rafa Nadal avoided matching his worst ever losing sequence with a 7-5 7-5 victory over Norway's Casper Ruud in round-robin play at the ATP Finals on Thursday.
In a clash of tournament debutantes neither Fritz nor Auger-Aliassime could make inroads on the other's serve but in the first set tiebreaker, the Canadian's normally solid backhand began to misfire and a forehand error put Fritz out ahead.
The players remained on serve in the second to bring about another breaker that Fritz appeared to have in hand while leading 4-2.
But an errant ball toss produced Fritz's first double fault and shifted momentum in favour of Auger-Aliassime, who pumped his fist after slapping a crosscourt winner to force a deciding set.
The key game of the match came with Fritz leading 3-2 in the third when he finally got his first looks at break points, converting his fourth opportunity when Auger-Aliassime pulled a forehand wide.
Fritz rolled from there, holding to love to consolidate the break and jumping in the air when Auger-Aliassime pushed a backhand out on match point, his 36th unforced error.
"It was tough, no one really had any chances early on," Fritz said after his 7-6(4) 6-7(5) 6-2 win.
"I had to just not get frustrated, had to reset. I felt going into the third that a break was coming."
Fritz will face Novak Djokovic in the semi-finals.
Nadal had already been eliminated from semi-final contention when he walked on court in Turin after back-to-back straight-sets defeats in the Green Group by Fritz and Auger-Aliassime.
But the Spaniard was clearly eager not to end a season that began in such spectacular fashion by succumbing to a fifth successive defeat -- something the 36-year-old had not experienced since before his career took off in 2004-05.
The first set was full of intensity inside the Pala Alpitour where the afternoon crowd were firmly behind Nadal.
Nadal fought off two break points at 4-4 in the opening set as Ruud threatened but after that the Mallorcan found the range on his forehand.
The 23-year-old Ruud went down 0-40 on serve at 5-6 and world number two Nadal needed just one chance to seal the set, punching away a volley into an empty court.
It was a similar story in the second set with nothing between the players until Nadal pounced again in the 12th game.
Ruud saved one match point but Nadal clubbed away a backhand winner to finish his season on a high.
"I've been practising well but just not had enough matches to be at the level I need to be, not enough confidence after six tough months," Nadal said.
"At least I finished with a positive victory which is important."
Ruud still advanced to the semi-finals but is now 0-8 against opponents ranked in the top three.