Michael Jamieson set the fastest time in the world this year of two minutes 7.78 seconds in the 200m breaststroke final at the British Championships.
The Olympic silver medallist, 24, had been worried he may have to withdraw from the trials with a biceps tear.
Jazmin Carlin (women's 1500m) and Ben Proud (men's 50m butterfly) clocked British records in their events.
Meanwhile, Marco Loughran defeated two-time world champion Liam Tancock in the 50m backstroke final.
Jamieson was second to Bath University team-mate Andrew Willis, 22, at the halfway stage but hauled himself clear in the closing stages as both swimmers secured the time they required to make next month's World Championships squad.
"I honestly don't know where that came from," Jamieson told BBC Sport.
"The support staff in Bath have done an amazing job and I've been seeing the doctor every day which has obviously made the difference. I was just looking to get the qualifying time and second place because I know Andrew's in great form.
"I haven't been able to go in the gym for the past month and the muscle falls off if I'm not lifting, so fingers crossed it's on the mend and I can get some good training in before the worlds."
"I've actually forgotten how much the 1500m hurt," admitted Carlin, who is likely to opt against swimming the event in Barcelona and focus on the shorter distances.
"Last year was really tough but when you come back and you do best times it makes it worth it and I hope my family are proud."
The previous British men's 50m butterfly record was held by Mark Foster, whose time of 23.51 seconds was set back in 2003, but 18-year-old Proud beat that twice in the same night.
The Plymouth-based swimmer recorded 23.29 in the semi-finals before lowering that to 23.10 in the final.
"I'm really happy with that. To beat Mark Foster's record is amazing especially as I was just eight years old when it was set," Proud told BBC Sport.
Tancock, who won 50m backstroke gold at the 2009 Rome and 2011 Shanghai World Championships lost the 100m final to Chris Walker-Hebborn on Thursday and admits he does not expect to be allowed a defence of his world crown after losing to Loughran, 24.
The 28-year-old Loughborough-based swimmer added: "It's not down to me, it's down to the selectors but I've given it my best this week and I know I'll come back stronger."
Welsh Commonwealth swimmer Loughran was delighted with victory, especially as he is not funded by British Swimming.
"It may not have got me to the worlds as it's a non-Olympic event but just to be noticed and prove a point shows I'm doing something right," he said.
Elsewhere, London Olympian Stacey Tadd won the 50m breaststroke final in 31.75, which was just two one-hundredths ahead of Kathryn Johnson, on a busy night for the Bath-based swimmer, who also qualified for Saturday's 200m individual medley final.
Scottish Commonwealth champion Robbie Renwick followed up securing a 400m freestyle World Championship berth on Wednesday with a second after victory in the 200m freestyle final in 1.46.63.
The women's 200m freestyle was won by Eleanor Faulkner and although the time of 1.58.42 was not enough for Barcelona, the teenager was content after securing her place in the 800m event on Thursday.
Paralympic champion Jessica-Jane Applegate, 16, added another title to her collection with victory in the 200m individual medley, clocking a personal best of 2:34.69 in beating Natalie Massey and Ellie Simmonds.
Applegate had already set a personal best to win 200m freestyle gold at the meet - and Ben Proctor, 23, also claimed his second gold in two days, winning the men's 200m individual medley in 2:19.88.
Twelve-time Paralympic medallist Matthew Walker took gold in the men's 50m butterfly final in 32.75, finishing ahead of Andrew Mullen (40.10).
Walker, preparing for his fifth IPC World Championships this summer, said: "That time was the same as when I tapered in April so out in Montreal I want to go quicker again."
Highlights on the penultimate night of the British Swimming Championships include Olympic finalists Elizabeth Simmonds and Jemma Lowe bidding for World Championship qualification after missing their targets in their favoured events earlier in the week.
Jamieson will also return for the 100m breaststroke, while 50m freestyle champion Francesca Halsall should compete over 100m.