Alexander Zverev faltered just once when Novak Djokovic broke him early in the second set but that was the only blemish on an extraordinary performance.
Some fans booed the Alexander Zverev after his superb victory over Roger Federer in the last four of the ATP Finals.
Novak Djokovic is eyeing a record-equalling sixth end-of-season title at London's O2 Arena.
Alexander Zverev, who has three Masters series titles, is the youngest finalist at the event since Juan Martin del Potro in 2009.
Novak Djokovic has enjoyed a remarkable renaissance in the second half of the season after an elbow surgery.
Alexander Zverev is the youngest semi-finalist at the ATP Finals since Juan Martin del Potro in 2009.
Novak Djokovic is chasing a sixth ATP Finals title and his first in the prestigious season-ending event at London's O2 Arena since 2015.
Roger Federer and Novak Djokovic, along with six fellow tennis stars travelled to Westminster by the London Underground.
Roger Federer has not been at his best all week, dropping sets in the two opening matches of his wobbly title defence.
Novak Djokovic is in sparkling form, winning Wimbledon, the Cincinnati Masters and US Open in recent months, after having elbow surgery in February.
Earlier this week, Fernando Verdasco had berated a ball boy at the Shenzhen Open for failing to bring his towel fast enough.
The hilarious incident that took place during a Shanghai Masters match was caught on camera and quickly went viral.
Alexander Zverev smashed his racquet in frustration after losing to Malek Jaziri.
Alexander Zverev came from a set down to beat Kevin Anderson as the Europeans successfully defended the title won in Prague last year.
Roger Federer will be seeking a 13th appearance in the US Open quarter-finals when he plays Australian John Millman.
Federer, the second seed, escaped the worst of the conditions as he headlined the night session on Ashe.
Novak Djokovic called for the doctor during the second set against Adrian Mannarino but put aside his discomfort to progress 4-6, 6-2, 6-1.
The world number one Spaniard was untouchable as he schooled Paire for the fourth time without a loss, taking 74 minutes as he broke six times.