Juan Martin del Potro said that he was battling illness after he suffered a shock defeat in the China Open final on Sunday, losing 6-4, 6-4 to unseeded Nikoloz Basilashvili of Georgia.
In the women's final, world number two Caroline Wozniacki defeated Latvia's Anastasija Sevastova 6-3, 6-3 for her 30th WTA singles title.
Argentine top seed Del Potro was far from his best and has been fighting flu or a cold for several days in the Chinese capital.
The world number four said that he did his utmost in difficult circumstances.
"I did everything that I can to be better for the final, it wasn't enough time to feel 100 percent," the 30-year-old said.
There was to be no surprise in the women's decider.
Denmark's Wozniacki was impressive all week, never dropping a set and rarely looking troubled, sealing her spot in the WTA Finals Singapore in the process.
The 28-year-old, who won her first Grand Slam at the Australian Open at the start of this year, was imperious against the unseeded Sevastova.
It is her second China Open crown — she also won it in 2010 — and 30th overall.
"I'm just happy to have reached 30 today, I'm going to enjoy that," said Wozniacki, a former number one.
"As a little kid I had a dream of becoming a professional tennis player, becoming number one in the world.
"Then after number one in the world, I wanted to win a Slam, then I wanted to lift trophies.
"Having done everything, all of that, it's pretty amazing.
"I think I had a dream of that, but I don't know how realistic I really believed that was going to be."