Christine Ohuruogu gave herself a huge boost ahead of the World Championships with a winning 400m time of 50.56 seconds in a warm-up race in Osaka.
Ohuruogu has been in training at the GB camp in Macau
The 23-year-old Briton, whose ban for missing three out-of-competition tests expired last week, clocked the fastest outdoor time by a Briton this year.
Ohuruogu's 400m heat is on Sunday, and her coach Lloyd Cowan said: "She was nervous but it was a good workout.
"We have a job to do here and we're looking forward to next week."
BBC Radio 5live's Mike Costello said: "Given her absence of a year or more it was an astonishing performance.
"She and her coach Lloyd Cowan couldn't have hoped for any more than this."
The tension was clear to see on Ohuruogu's face as she went to the blocks, but Costello added: "You could tell how significant this was as part of her build up to the World Championships.
This was a performance to suggest that, when fully fit, Ohuruogu has more to come
BBC Radio 5live's Mike Costello
"It was a brilliant run, quicker than British champion Nicola Sanders this year and the best outdoors by a Briton since she herself won the Commonwealth title in Melbourne in March 2006.
"The time would also have been good enough for fifth pace in the Worlds two years ago in Helsinki."
Ohuruogu was watched by a group of her fellow British athletes and coaches and was greeted with cheers and applause as she crossed the line.
It was one of several races taking place in the Nagai Stadium in Osaka enabling officials to check that events will run smoothly when the championships get under way on Friday.
Also running were fellow Briton Donna Fraser and American Monique Hennagan, the 2003 world indoor bronze medallist and part of the US team that won 4x400m relay gold in 2000.
And Costello added: "What was most impressive was the controlled nature of the race, allowing her to take the lead and surge clear in the home straight.
"This was a performance to suggest that, when fully fit, Ohuruogu has more to come, if not here then in Beijing next year."