Now you see him, now you don't.

China's top sprinter Su Bingtian has the ability to run the 100m faster than his personal best of 9.91 seconds, said his coach Randall Huntington at the national trials on the weekend.

The 29-year-old Su twice ran 9.91 last summer to equal the Asian record, setting another career milestone after becoming the first Chinese to break the 10-second barrier in Eugene, Oregon, in 2015.

But Huntington, former coach of long jump world-record holder Mike Powell, is confident his protege can run even faster.

"Su's ability shows he can run faster than 9.91. I'm not going to predict whether he will or won't, because it's all going to depend on what he does in that particular race. Right now the elements are coming together for him to run faster... but it's going to take more races," said Huntington, who joined Su's coaching team in late 2017.

In his first race since being sidelined with a back injury in May, Su, who secured a berth at the upcoming IAAF World Championships in Doha before the two-day national trials, clocked 10.19 to finish second to Xie Zhenye in Friday night's 100m final.

Xie, who set an Asian men's record in the 200 by clocking 19.88 at an IAAF Diamond League meet in London last month, overtook Su in the final stretch to win in 10.03. "Su's start was top notch, so I needed to make up for my disadvantage at the start with better acceleration in the latter half," said 25-year-old Xie.

Su was satisfied with his finish, saying: "I haven't competed for a while so I need time to adjust. The first half of the race was fine, but when Xie caught up with me, it was like the Asian Games all over again. I was in better form, but tonight my body felt a bit stiff.

"I don't think the long break from competition will affect me much, but I do need more races."

Huntington said it will take time for Su to readjust to competition.

"While we were training in Switzerland we went to Roger Federer's doctor, who is a back specialist. He did an incredible job," said the American.

"This race was a test event because we've been working on many technical aspects of Su's 100.It was his first opportunity to actually get out and try some of those things," added the coach.

Su will turn 30 this month, but Huntington believes he still "has plenty of gas in the tank".

"He's not that old. He'll be 30 at the end of the month. Look at (Justin) Gatlin, look at Carl Lewis. Those guys raced until their late thirties," he said.

Gatlin stunned Jamaican legend Usain Bolt in the 100m final to be crowned 2017 world champion at age 35 while Lewis retired at 36 with nine Olympic gold medals and eight world titles.

"Su has plenty of gas in the tank to get him to Tokyo, and I'm not killing him in training. His body is not getting beat up," said Huntington.

Happy hurdler

Meanwhile, after breezing to a convincing victory at the national qualifiers, 110m hurdler Xie Wenjun will be gunning for his first top-eight finish at the worlds in Doha.

"Making it to the final at the world championships has always been my goal and this time I will be pursuing it with greater confidence," said the world No 3 after clocking 13.43 sec at Shenyang Olympic Stadium.

"My coach did not set any goal for today's race, so I was competing with entirely no pressure."

The 29-year-old Shanghai native has had an impressive season, twice improving his personal best to 13.17 and claiming the title at the London leg of the IAAF Diamond League last month.

"I have learned a lot from elite hurdlers like Sergey Shubenkov and Omar McLeod while competing against them," said Xie.

"Beating them at a Diamond League event is really a boost of confidence for me. I started to train under the guidance of my current coach (Rana Reider) last year and he has helped me to change a lot both mentally and in terms of techniques. That's the secret of my progress."

Xie failed to pass the preliminary round at the Moscow worlds in 2013 and was eliminated in the semifinal phase at the 2015 and 2017 editions in Beijing and London.