Competing just three days after winning his first ATP Masters 1000 title in Toronto, Shelton was leading 6-3, 3-1 after 64 minutes when the Argentine retired.<\/p>\r\n\r\n
Carabelli grasped his knee on the first point of the fourth game of the second set after an awkward movement coming forward into the court. After a medical timeout he could not move freely and retired after completing Shelton\u2019s service game, ATP reports.<\/p>\r\n\r\n
\"I feel for Camilo and it\u2019s obviously not the way that you want to go through. I hope that he has a quick recovery,\" Shelton next faces Spanish veteran Roberto Bautista Agut, said.<\/p>\r\n\r\n
Meanwhile, world No. 3 Alexander Zverev dropped a serving masterclass on American Nishesh Basavareddy to breeze into the third round with a 6-3, 6-3 win, his 40th of the year.<\/p>\r\n\r\n
Zverev said that he was happy to get through without expending too much energy, and to avoid playing in the heat of the day.<\/p>\r\n\r\n
\"I requested (a night match), coming from Toronto, where it\u2019s a lot colder, I need some days getting used to the heat and conditions. I\u2019m happy with the win and happy with how I played.\"<\/p>\r\n\r\n
The two-time ATP Finals champion will next play 27th seed, American Brandon Nakashima, who toughed out a 4-6, 6-3, 7-6(5) win over Belgian qualifier Alexander Blockx.<\/p>\r\n\r\n
\"I requested (a night match), coming from Toronto, where it\u2019s a lot colder, I need some days getting used to the heat and conditions. I\u2019m happy with the win and happy with how I played.\"<\/p>\r\n\r\n
The World No. 12 hit seven aces according to ATP Stats and took charge with his forehand in his one hour, 50-minute win. He next faces American wild card Jenson Brooksby.<\/p>\r\n\r\n