Ukrainian Mykhailo Romanchuk made a statement at the World Swimming Championships on Monday morning as he grabbed a narrow edge in the 800m men's freestyle heats.
Romanchuk, twice a silver medallist in the worlds and once in the Olympics, is Ukraine's best hope of a gold in the worlds.
He trailed in fourth early on in a high-powered third heat. He surged through late in the race to win in 7min 44.75sec, edging German Florian Wellbrock, the Tokyo open-water gold medallist, by 0.05sec.
Italian Gabriele Detti, who won the event when the championships were last in Budapest in 2017, was third.
On a good morning for Italy, Gregorio Paltrinieri won the depleted final heat to qualify fourth.
Elijah Winnington, who won the 400m free on Saturday, and Austrian Felix Auboeck, who was fourth in that race, were late scratches from the heats.
The two men will race in the 200m freestyle final, which opens Monday evening's action.
One the 200m finalists who did race, but not very well, was German Lukas Martens. The silver medallist in 400 had a horrible swim, finished seventh in the last heat and failed to qualify.
The morning opened with Nicolo Martinenghi showing no Monday morning hangover from his intoxicating 100m breaststroke victory the night before.
A couple of minutes over 15 hours after his first major gold medal, the Italian was back in the pool and outpacing his breaststroke rivals.
He swam 26.68, 0.2sec ahead of American Michael Andrew with Brazilian Joao Gomes third and Sunday's bronze medallist American Nic Fink fourth.
A small eddy of controversy continued to whirl round the breaststroke, as eight of the 66 entrants were disqualified. None were serious medal contenders.
While no immediate reason was given, organisers announced that they would be hearing an appeal by American breaststroke swimmer Annie Lazor against her disqualification the day before for a "non-simultaneous" kick.
Unless over-turned, that decision will cost Lazor a place in the 100m final on Monday evening.
Another of the young breakout swimmers of the opening weekend, French medley specialist Leon Marchand, also advanced to a semi-final on Monday morning, although in more low-key style.
The 20-year-old, who won the 400m medley on Saturday, finished 11th best in the men's 200m butterfly heats.
He was 2.28sec behind the fastest man, Kristof Milak, the hosts best hope of a gold in these championships. Milak only turned up the heat on the last lap as he burned off the opposition.
South African star Chad Le Clos was a late scratch.
In the women's 200m freestyle, the leading contenders measured their efforts in the absence of the Olympic gold and silver medallist. Australian Ariarne Titmus is skipping the championships and Hong Kong's Siobhan Haughey, who has been struggling with an ankle injury, scratched on Monday morning.
China's Yang Junxuan, who was quickest, and Australian Madison Wilson were the only two women to swim under 1min 57sec.