Two teenagers and a 20-year-old won the three individual men's events, another teenager was in Britain's gold-medal relay team, and a 16-year-old Italian took bronze in a race in which he did not expect to swim.
Kristof Milak (HUN - pictured top), who won four golds at the junior world championships last year, was inside Michael Phelps's nine-year-old world record at halfway in the 200m butterfly. The 18-year-old faded in the last 50m but his time of 1 minute 52.79 seconds was further evidence that he has eclipsed his team-mate Laszlo Cseh (HUN), a six-time Olympic medallist and the oldest man in these Championships at 32. Cseh did not make the final but Hungary still had a 1-2 when 21-year-old Tamas Kenderesi (HUN) was second.
Third place went to Italy's 16-year-old Alessandro Burdisso, who came in as a reserve when James Guy (GBR) withdrew to focus on the next event, the 4x200m freestyle relay, which started seven minutes later.
"It's amazing - I am very lucky," said Burdisso, one of five Italian medallists on a night of six finals.
Guy and his British team-mates, including 18-year-old Tom Dean, won the relay ahead of Russia - who also had a teenager in their team - and Italy.
The third teenage gold medallist was Alessandro Miressi (ITA - pictured inset), who held off the home crowd's favourite Duncan Scott (GBR) and the Frenchman Mehdy Metella (FRA) in a tight finish to the men's 100m freestyle. Miressi, 19, is a former European junior champion at the distance.
Florian Wellbrock (GER) was a surprise winner of the men's 1500m, in which the Italian favourite Gregorio Paltrinieri (ITA) finished only third, having felt unwell before the race. It was Paltrinieri's first defeat over the distance since the 2013 World Championships. Wellbrock improved his semi-final time by nearly 20 seconds and said: "Today I didn't focus on my times. It was much more a race swum in the head rather than with the arms."
By comparison the two women's winners were veterans as 27-year-old Georgia Davies (GBR) won the 50m backstroke and Yuliya Efimova (RUS) took the 100m breaststroke. That gold for Efimova, 26, kept Russia top of the medals table.