Top seed Andy Murray cruised to a 6-2, 7-5 victory over Andreas Seppi in the first round of the China Open in Beijing on Tuesday, while No. 4 seed Dominic Thiem was upset by Alexander Zverev in three sets 4-6, 6-1, 6-3.
No. 2 seed Rafael Nadal dominated Paolo Lorenzi 6-1, 6-1 as he tries to secure his spot in the season-ending ATP World Tour Finals, while No. 3 seed Milos Raonic of Canada advanced with a 6-4, 7-6 (1) victory over Germany's Florian Mayer.
Unseeded American Jack Sock defeated China's Ze Zhang 6-3, 7-5 and Andrey Kuznetsov beat Konstantin Kravchuk in a battle of fellow Russians.
Murray said he is past a shoulder injury that first began to bother him in August and will face Kuznetsov in the second round.
"I thought I did okay considering I hadn't played much the past couple of weeks. I think I can do better," said Murray. "But there was some good stuff in there. With each match, I'll play better hopefully. No injuries. Felt fine. Just need matches now."
Meanwhile, Nadal awaits the winner of Albert Ramos-Vinolas and Adrian Mannarino as he seeks his third ATP World Tour title of the season. Nadal currently sits in the final qualifying spot in eighth place.
"Today is an important victory," he said. "There are points to try to qualify for the (Barclays ATP) World Tour Finals."