Instead, an oblivious Federer returned to the baseline after clinching a final spot in Halle as Nishikori awkwardly paced around the midcourt.
It eventually dawned on the former world number one that the match was over and he apologetically raised his hands and jogged towards the net to celebrate his 6-4 7-6(4) win.
Watch the comical ending below:
"It was the first time in my career in over a thousand matches," Federer, who has played 1178 tour-level matches, admitted after the match.
Federer will face world number 69 Alejandro Falla in the final.
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- Roger Federer
- Kei Nishikori