By Martyn Herman
LONDON (Reuters) - A few hours after old master Roger Federer reminded everyone of his enduring magic, Alexander Zverev, the man leading the next generation of men's tennis, dazzled on his ATP Finals debut.
The 20-year-old German, ranked three in the world, was hot and cold against Croatia's Marin Cilic but, when it mattered most, he produced his best tennis to win 6-4 3-6 6-4.
Zverev, the youngest qualifier for the season-ender for nine years, appeared to be fading after a dazzling start, but surged back in style to join Federer on top of Boris Becker Group.
"It is different walking on here than any other stadium. The crowd, the atmosphere is amazing," Zverev, who reveled on the big stage, told reporters after the late-night finish.
"There were a lot of nerves involved in my first match. Obviously I'm happy that's behind me. I'm happy that I won."
Zverev possesses huge power off the ground, yet it was his finesse at the net which earned him a break in the opening game, picking off a low drop volley that gave Cilic no chance.
His forehand wavered at times as Cilic cleverly tried to take the pace off the ball with some floaty slices, but Zverev closed out the first set with an ace.
Cilic, back in London since his traumatic Wimbledon final defeat by Federer when he broke down in tears as blisters wrecked his big day, then took control.
The big Croat upped his serving and forehand power to level the match and then led 3-1 in the third set.
At 3-2, he was 40-15 up on serve but Zverev, wound-up by an erroneous over-rule, forged back to break with an exquisite lob.
Cilic then dropped serve to love at 4-5 to lose for the sixth time in seven matches at the year-ender.
Zverev, bidding to become the first German to finish the year in the world's top three since Boris Becker in 1994, will face a mouthwatering clash with Federer on Tuesday.
Six-times champion Federer had earlier beaten Jack Sock.
"I think anyone beating Federer in this group has a good chance of (reaching the semi-finals)," Zverev, who beat the Swiss to win this year's Montreal title, his second Masters 1000 title of the year, said.
"But he's the favorite definitely in all of the matches he plays. But I enjoy playing in front of big stages, big crowds."
(Reporting by Martyn Herman, editing by Pritha Sarkar / Ian Ransom)