Budapest - Caeleb Dressel can make history on Sunday by matching Michael Phelps's feat in winning a seventh gold medal at a world aquatic championships.
The 20-year-old Dressel claimed three world golds within an hour and a half on Saturday.
Victories in the men's 50m freestyle and 100m butterfly, then with the USA team in the mixed 4x100m freestyle relay, leaves him with six golds in Budapest.
Dressel can match Phelps' record of seven gold medals, from the 2007 world championships in Melbourne, with victory in the men's 4x100m medley relay on Sunday.
Despite the physical and mental toll of winning three world golds within 90 minutes, Dressel is relaxed before Sunday's final day.
"I don't feel under pressure," he said.
"I just want to keep doing my own thing and I'm looking forward to that one more fast one."
Elsewhere on Sunday, Russia's Yuliya Efimova and America's Lilly King will resume their battle in the 50m breaststroke final.
Honours are so far even in Budapest.
King won the 100m final in a new world record on Tuesday, when Efimova took bronze.
The Russian then gained revenge with a commanding display in Friday's 200m final when her rival faded to fourth.
The pair were the fastest qualifiers into Sunday's final as King clocked a new Americas record of 29.60 seconds, but Efimova was just 0.13 behind.
Ruta Meilutyte's 50m world-record of 29.48 seconds, set four years ago in Barcelona, could fall.
Sarah Sjostrom of Sweden set a new world-record for the women's 50m freestyle by clocking 23.67 secs in Saturday's semi-finals.
She will be bidding for her third individual gold of these world championships after victory in both the 50m and 100m butterfly.
The 23-year-old became the first woman to swim the 100m freestyle in under 52 seconds with a new world-record of 51.71 last Sunday.
Sjostorm also holds world-records in the 50m butterfly.
"I'm really happy I could erase one of those textile-suit records," said Sjostrom her 50m freestyle time broke Brita Stefan's previous record set in 2009.
"A lot of people thought those times from 2009 would be impossible to beat."
Home-crowd favourite Katinka Hosszu can win her second individual medley title of these championships in the women's 400m final.
The 28-year-old won gold over 200m earlier in the week and can complete the IM double in the 400m final to defend the titles she won two years ago in Kazan.
Hungary's 'Iron Lady' took silver in the women's 200m breaststroke final on Saturday behind Australia's Emily Seebohm.
Hosszu already has the full set of medals in Budapest after bronze in the women's 200m butterfly.