Dai Greene beat Welsh rival Rhys Williams in the final of the 400 metres hurdles in the on Saturday in 48.66 seconds.
But Williams ran a personal best 48.85s in Birmingham to secure World Championship selection after briefly seeming to lead the final.
Brett Morse also ensured a World Championship discus place with a winning 62.05m first-round throw.
Wales' Lee Doran took the javelin title with a 70.77m fourth-round throw.
In the 800m, Gareth Warburton finished third in 1:49.62 with fellow Welshmen Joe Thomas seventh in 1:49.62 and Joe Maynard eighth and last in 1:50.69.
As reigning world champion, Swansea Harrier Greene was already guaranteed the chance to defend his title in Moscow on 10-18 August.
Greene competed at the trials in a bid to run himself into form after a torrid season so far.
Williams had handed Greene his first defeat by a fellow Briton in five years on this track at the Diamond League meeting 12 days ago.