World number one Novak Djokovic's bid for the calendar grand slam is under way, although not without a fright.
The 20-time major champion dropped the second set to 18-year-old qualifier Holger Rune, and only a nasty bout of cramp prevented the youngster inflicting more damage.
Ashleigh Barty also got off to a winning start against Vera Zvonareva in straight sets.
Meanwhile, Britain's Emma Raducanu followed up her remarkable run to the last 16 at Wimbledon with another impressive display at a major to beat an opponent 13 years her senior.
Here, the PA news agency looks back at day two at the US Open.
Picture of the day
Tweet of the day
Fact of the day. It takes Stefanos Tsitipas twice as long to go the bathroom as it takes Jeff Bazos to fly into space. Interesting. 🚽 🚀
— Andy Murray (@andy_murray) August 31, 2021
Andy Murray doubled down on Stefanos Tsitsipas and bathroom-gate following his controversial defeat on Monday.
Shock of the day
In-Cress-ible!
🇺🇸 Maxime Cressy delivers the biggest upset of the 2021 #USOpen pic.twitter.com/3nysnRbO1U
— US Open Tennis (@usopen) August 31, 2021
Ninth seed and Olympic bronze medallist Pablo Carreno Busta was a surprise first-round casualty, losing a deciding set tie-break against American Maxime Cressy.
Stat of the day
Quote of the day
Is that Sue Barker?
bark if you're excited to see the top player in the world in action pic.twitter.com/a6UCOEd985
— US Open Tennis (@usopen) August 31, 2021
Brit watch
What a moment. @EmmaRaducanu claims her 1st win at the #USOpen
🎥 @primevideosport pic.twitter.com/XZRxE38z6l
— LTA (@the_LTA) August 31, 2021
Raducanu is through to round two on her overseas grand slam debut after beating the experienced Stefanie Vogele of Swtzerland 6-2 6-3. She will face China's Zhang Shuai on Thursday. But Katie Boulter was unable to follow suit, bowing out 6-3 6-2 against Russia's Ludmilla Samsonova.
Fallen seeds
Men: Pablo Carreno Busta (9), Alex de Minaur (14), Lorenzo Sonego (20), Karen Khachanov (25), David Goffin (27), Fabio Fognini (28).
Women: Veronika Kudermetova (29).
Up next
Third seed Tsitsipas is back in action against Adrian Mannarino of France, while Naomi Osaka opens things up on Arthur Ashe against Serbia's Olga Danilovic.
The last British man standing, Dan Evans, takes on American Marcos Giron first up on Court 10.
