Berlin- Eight-time champion Roger Federer and Alexander Zverev clash in a battle of generations on Sunday in the final of the Halle tournament with the Swiss superstar looking to make a mockery of their 15-year age gap.
Federer, 35, despatched Russian Karen Khachanov 6-4, 7-6 (7/5) on Saturday to move into the final.
The world number five, building up to an assault on an eighth Wimbledon title in July, will now face German fourth seed Zverev who saw off France's Richard Gasquet 4-6, 6-4, 6-3.
Federer has yet to drop a set in Halle where he was playing his 13th consecutive semi-final on Saturday.
"I thought it was extremely close, especially that second set. I'm still just very happy how I was able to close it out in the tiebreaker," said Federer, who first reached the Halle final in 2003 -- when his opponent on Sunday was just six.
"It was perhaps not always very beautiful to watch, but it's good to be in the final in the second tournament after my return."
Federer defeated Zverev's older brother Mischa in the second round this week.
However, he was defeated by Alexander Zverev in three sets in the semi-finals at Halle in 2016.
Federer, who won an 18th major at January's Australian Open, skipped the entire clay court season to preserve his powers for the grass campaign.
His return in Stuttgart was brief as he lost first up against close friend Tommy Haas, the world number 302.
"I was a little uncertain about a player I don't know too well," he said of Khachanov.
"I really had to fight in defence, but maybe it's not so bad to survive like this on grass."
Zverev, 20 and the youngest player in the world top 40, is looking to make the Halle final for the second successive year after losing to compatriot Florian Mayer in 2016.
"Roger is the best player of all time on grass, it will be a very difficult match," said the young German.