Australian Open: US 20-year-old Michelsen upsets Tsitsipas as Tiafoe overcomes vomiting spell

• Michelsen beats No 11 seed in four sets
• Tiafoe grinds out five-set victory despite illness

Alex Michelsen produced the biggest win so far of his fledgling career to upset 2023 runner-up Stefanos Tsitsipas in the first round of the Australian Open, and he knew instinctively where credit was due.

The 20-year-old American overcame nerves on his serve in the fourth set before clinching a 7-5, 6-3, 2-6, 6-4 win on Monday over Tsitsipas, the No 11 seed at this year's tournament.