In the second round, there was a loss against only 20-year-old Canadian Felix Auger-Aliassime with the numbers 4-6, 6-3, 6-2.
The 20-year-old describes Federer as his childhood idol and the victory is his biggest in his career.
- This was not something I expected.
It's a huge honor to play against him before he stops playing, and to beat him feels great.
It is something I will always remember, he says.
Roger Federer has previously won the ATP tournament in Halle ten times.
It now remains to be seen if he finds his way back to form ahead of Wimbledon, which starts on June 28.
ARCHIVE: Djokovic: "One of the matches I will always remember in the future" (June 12)
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Djokovic took a heavy victory against Rafael Nadal - after a phenomenal match.
Photo: TT