Beijing: Rafael Nadal stuttered to victory against one of his former ball boys at the China Open as top-ranked Novak Djokovic swept imperiously to his 25th straight win in Beijing.
Out-of-sorts Nadal was broken four times by China's 230th-ranked Wu Di, who once tossed him balls and towels in Shanghai, before winning an error-strewn match 6-4, 6-4.
Nadal, 29, was playing for the first time since his third-round defeat at the US Open, but it was a far from satisfying return as the 14-time Grand Slam-winner continued to grope for form.
"We don't need to talk more about confidence, rhythm.
That's my level today, and I'm going to work hard to try to improve my level of today," he said, after reaching the second round.
"But tomorrow is another opportunity. I played a match today that I can play better, and I think I can play better tomorrow because I'm practising well."
On a heavily polluted day in Beijing, Wu anticipated superbly when he lunged for a forehand volley winner for his first break of the Spaniard early in the first set, and he wasn't done yet.
Wu broke again to go ahead in the second set but with both players uncomfortable on serve, Nadal was able to wrap it up after 86 minutes and progress to a second-round meeting with Vasek Pospisil.
"I'm practising well, so the level of tennis is going to be there sooner or later. I am working a lot to make that happen. I think I'm closer to that," Nadal said.
"I know it's obvious that I need results to confirm that.
But we are almost at the end of this season and I have time to keep playing the last tournaments of the year with the chance to practise the things that I need to do for next year.
"My goal is recover the level especially to play my best on clay next year."
Nadal and Wu then yielded the smoggy centre court to Djokovic and the Serb, fresh from winning his 10th Grand Slam title in New York, had little difficulty dispatching Simone Bolelli 6-1, 6-1.
The five-time champion was all over Bolelli's second serve as he hustled the Italian off the court in just 71 minutes to take his incredible unbeaten record into a sixth China Open campaign.
It was an afternoon which underlined the gulf that has opened up between Djokovic and Nadal, once his close rival but now down to eighth in the world and a shadow of his fearsome best.
Nadal is using the year's final events as practice for next season, after a forgettable 2015 in which he didn't progress beyond the quarter-finals of any of the Grand Slams.
As for Wu, 24, it completed a journey after he was a ball boy for the Spanish great at the Tennis Masters Cup in Shanghai, and later progressed to become his practice partner.
"As for the ATP Finals (Tennis Masters Cup), I served as the ball boy for Rafa. So right now I played Rafa. It's not a small deal," he said.