Greene is the fastest man in Europe this season
David Greene won the 400m hurdles final at the UK Athletics Championships in Birmingham, beating fellow Welshman Rhys Williams into second place.
Greene's time of 49.07 seconds sees him qualify for next month's world championships in Berlin, but Williams has yet to attain the necessary time.
"I'm pleased to come away with the win and, obviously, qualification for Berlin," said Swansea's Greene, 23.
"It adds to my confidence no end, there were some good athletes in that race."
Greene is the fastest man in Europe this season after running 48.62 in Prague last month.
I've had a few different coaches in the last few years and they've all brought something different
A foot tendon injury has hampered his progress over the last 18 months and he has shuttled between different coaches, but Greene says that has helped his recent success.
"I've had a few different coaches in the last few years and they've all brought something different," he told BBC Sport.
Greene's win followed Welsh success for Philippa Roles on Saturday.
The 31-year-old's season-best throw of 57.57 metres secured her a fifth AAA discus title.
Newport sprinter Christian Malcolm had a poor championship, though.
The 30-year-old failed to make Saturday's 100m final.
The defending 200m champion qualified for Sunday's final in that event, but finished a disappointing fifth in 21.18 secs.