Taylor Fritz is the first American since 2006 to reach the title match at the ATP Finals, winning a slugfest against world No. 2 Alexander Zverev.
Imperious home favourite and world number one Jannik Sinner outclassed Norway's Casper Ruud to set up an ATP Finals title decider against Taylor Fritz on Saturday.
Sinner was unstoppable as he dispatched Ruud 6-1, 6-2 in the evening session at a packed Inalpi Arena and will be favourite to become Italy's first winner of the prestigious year-ender.
The second semi-final was a stark contrast to the first in which Fritz and world number two Alexander Zverev were involved in a ferocious slug fest, the American winning 6-3, 3-6, 7-6(3).
Fritz is the first American to reach the final since James Blake in 2006 and will hope to become the first American to lift the trophy since Pete Sampras in 1999.
Sinner's stupendous year may have been clouded by an anti-doping controversy but on the court he is finishing the season like an express train and has won 25 of his last 26 matches.
The 23-year-old was razor-sharp against Ruud and was in complete control after breaking serve in the second game. He has reached the final without dropping a set.
"I raised my level and I was intense with each shot," Sinner, who beat Fritz in the US Open final and also in the group stage in Turin, said on court.
"It's a similar circumstance to last year. I'll just try to play my best tomorrow and hopefully it'll be a good day."
Sinner lost in the final to Novak Djokovic last year having beaten the Serb in an earlier group match.
"I've grown a lot as a player," added Sinner, who struck 23 winners in a one-sided contest.
Zverev, who won the Paris Masters in the build-up to Turin, looked like the biggest threat to Sinner's title hopes.
The 27-year-old German, twice a winner of the year-ender, had not reckoned on an inspired Fritz however.
Fritz had won his previous three matches against Zverev and played what he described as a "perfect first set" to move ahead.
Zverev hit back though to set up a deciding set and had enough chances to have taken the win.
Fritz got ahead in the tie-break and admirably held his nerve, clinching the win with a thumping forehand winner.
"I found myself in some tough spots in the third, both of us really started to get on each other's serve even more, said Fritz, who will end the year at a career-high world number four.
"I told myself just to give him nothing from the back."
Zverev did not find the level he achieved during the group phase but still looked the favourite in a third set full of lengthy rallies from the baseline.
Fritz looked in big trouble on serve at 2-2 when some errors looked like proving costly but he managed to hold serve from 0-40. Zverev then found himself in a big hole at 3-4 down as he went 15-40 but fought off the break points and then another one after a double fault to stay level.
Matching Zverev from the baseline throughout an enthralling match, Fritz showed great resilience towards the end and once he reached the tiebreak, the odds swung in his favour as his opponent began to run out of steam.
"I've been playing the top guys at the big events a lot lately," Fritz, who lost to Sinner in the US Open final, said.
"I'm getting more comfortable and confident in those moments."
In the doubles El Salvador's Marcelo Arevalo and Croatia's Mate Pavic, the top seeds, beat seventh seeds Harri Heliovaara (Finland) and Henry Patten (Britain) 7-6(1), 7-6(4) to set up a final against German duo Kevin Krawietz and Tim Puetz.
Krawietz and Puetz saved a match-point in beating Australians Max Purcell and Jordan Thompson 2-6, 6-3, 11-9.
