Question: who beat roger federer in the us open
[{'answer': 'Novak Djokovic', 'provenance': [{'wikipedia_id': '34006492', 'title': 'Djokovic–Federer rivalry', 'start_paragraph_id': 1, 'start_character': 90, 'end_paragraph_id': 1, 'end_character': 104, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]