Roger Federer downs Alexander Zverev in the battle of the generations
Roger Federer was pushed into a decider by Alexander Zverev at the ATP World Tour Finals, but then proved too strong in a 7-6 5-7 6-1 win.
The 36-year-old six-time champion may have been giving away 16 years to the man tipped to be the next superstar of the game but Federer proved in a dominant third set that for the moment he remains a cut above his young pursuers.
The triumph in 2 hours 11 minutes puts the 19-times Grand Slam champion in Saturday's semi-finals - the 14th time he has made the last four in 15 appearances - with the tournament still only three days old.
It also meant that Zverev and Jack Sock, who earlier battled from behind to beat Marin Cilic 5-7 6-2 7-6(4), will now meet on Thursday to decide the other qualifier from the Boris Becker group.
Federer's win ensured Cilic, once again a disappointment at the season-ending tournament, was eliminated. World number two Federer is now an overwhelming favourite for a seventh crown in the absence of Rafael Nadal, who has pulled out injured.