Federer and Zverev had already met in the O2 Arena - when the German's practice session overran and his opponent was forced to bounce on his toes for a few minutes while Juan Carlos Ferrero put his man through the last couple of serves.
Watch as they tackle some of the most famous phrases to come out of London's East End, with Federer's befuddled response to, "Blimey mate, I'm Hank Marvin" a particular highlight.
After those two games, the match zipped along at a rate of knots with barely 35 minutes having passed before Zverev was serving to try to force a tie-break.More news: Black worker says Tesla factory was a "hotbed for racist behavior"
"I think Jack is playing really good", Cilic said.
Both players were solid on serve until the 2014 US Open champion went 0-40 up when leading 6-5 and sealed the set when Sock stooped to drill a forehand low into the net.
Both players could ill afford another defeat after losing their first matches at the O2 Arena and there was a sense of deja vu for Cilic, who led Alexander Zverev 3-1 in the final set of his opening contest before being consigned to defeat.
Sock claimed five points in a row to set up two match points and he converted the first when a Cilic backhand floated long. The serve again dominated until the 12th game when, just as Zverev had in the first set, Federer faced set points on his serve. The Swiss world No 2 beat the German in Halle but Zverev returned the favour at the Montreal Masters.More news: With Cardiogram's AI, Apple Watch can detect sleep apnea, hypertension, study shows
Zverev will now play American Jack Sock for second place in the Boris Becker Group after the American - who revealed the fire alarm that disrupted Nadal and Dominc Thiem at an ungodly hour - upset Marin Cilic 5-7, 6-2, 7-6, thus eliminating the Croatian.
"It's been an interesting morning so far", said the American. My coach growing up nicknamed me "Showtime" because I love playing in front of people, and there is always a lot going on.
"But I love playing here in London, it's an wonderful atmosphere, you make me feel like home". As the world's most formidable player on clay, Nadal has in the past suggested it would be better if the season-ending Tour Finals at least occasionally took place on his preferred surface.
Novak Djokovic, Andy Murray and Stan Wawrinka are all long-term absentees from the Tour this season.More news: Eve Officially Joins 'The Talk' on CBS
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