Roberto Pavoni swam a lifetime best to secure British 200m individual medley gold and a place in the GB World Championships team.
Pavoni, 24, who claimed two European medals in 2014 but had his UK Sport funding axed later that year, won in a time of one minute, 57.79 seconds.
"I felt like I had a point to prove and I've done that," he told BBC Sport.
Jazz Carlin won 400m freestyle gold and qualified for the World Championships in Kazan, Russia.
Pavoni had won the 200m individual medley at each of the last two British Championships, but rival Dan Wallace had qualified quickest for the final at the London Aquatics Centre.
Little separated the two heading into the final length before Pavoni sprinted to victory, 0.66 secs ahead of Wallace, with Tristan Slater further back in third.
"I've never celebrated quite like that because it really meant everything," said Pavoni.
Carlin was the clear favourite for the women's 400m freestyle event - having won the race at each of the last two British Championships.
The Commonwealth and European champion set a time of four minutes, 3.51 seconds to finish ahead of Jessica Thielmann and Hannah Miley.
"There are lots of things that I've been working on in training and I'd like to think that there's more to come in terms of performance," Carlin told BBC Sport.
Pavoni and Carlin are the fourth and fifth swimmers to secure their places in the British team for the World Championships, following Adam Peaty, Chris Walker-Hebborn and James Guy, who attained theirs on Tuesday.
Welsh Commonwealth swimmer Calum Jarvis claimed a surprise victory over England's Benjamin Proud in the 100m freestyle final, with two-time winner Robbie Renwick third.
Scotland's Cameron Brodie won his maiden British title with victory in the 200m butterfly final, ahead of Jay Lelliott and Lewis Smith.
England's Molly Renshaw ended a run of three successive second place finishes at the British Championships, with gold in the 200m breaststroke.
However, her time of 2:25.75 was not enough for a place in Kazan; Katie Matts and Chloe Tutton were second and third respectively.
The 2015 British Championships - which run until Saturday evening - is the first elite swimming event to be held at the London Aquatics Centre since the 2012 Olympics.