Budapest - Caeleb Dressel is set to finish the world championships on Sunday with an historic seventh gold medal in Budapest as home-favourite Katinka Hosszu bids to live up to her 'Iron Lady' nickname.
Dressel won a jaw-dropping three golds in just an hour and a half on Saturday night, taking his total this week to six.
The 20-year-old can win a seventh of these championships in the men's 4x100m medley relay on Sunday -- the final event in Budapest.
Should the USA quartet win, Dressel would match Michael Phelps's record of seven from the 2007 worlds in Melbourne.
With Dressel rested for Sunday morning's heats, the US quartet were fastest into the final, clocking three minutes 29.66 seconds.
"It's unbelievable, me and Caeleb started swimming together when I was six years old and he was five," said Olympic backstroke champion Ryan Murphy, who swam the US team's first leg in the heats.
"This is probably one of the top-five best swim meets ever by an American male -- the other four going to Michael Phelps and Ryan Lochte.
"To be in that company is no small achievement, hopefully this is just the beginning for him and he can have a really great career."
The American female quartet were also the fastest into the women's 4x100m medley final just ahead of China and Canada, with Australia through as fifth.
Hungary's Hosszu was the fastest into the women's 400m IM final, clocking 4min 33.90sec in the morning heats.
Having already won the 200m IM title on Monday, Hosszu can complete the medley double with victory in the 400m final, having also won both world titles two years ago in Kazan.
In the men's 400m IM heats, Chase Kalisz is bidding to add to the 200m title he won on Thursday -- the eighth straight for the US in that event.
Kalisz clocked the fastest time into Sunday's 400m IM final of 4:09.79.
"It's been a long meet so hopefully I'll finish on a high note, that's my plan," said the 23-year-old.
Britain's Max Litchfield was second fastest at 0.78sec.
"It's going to be a tough race again, this is what you dream about doing, getting on the stage like this," said the 22-year-old, who finished fourth in last year's Olympic final.
The final session will start with a bang in the women's 50m breaststroke as America's Lilly King and Russia's Yuliya Efimova clash for the third and final time with honours even.
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 as her rival faded to fourth.
There is no love lost between the pair after King labelled Efimova a "drug cheat" at the Rio de Janeiro Olympics due to the Russian having served a 16-month ban for doping that ended in 2015.
The pair were the fastest qualifiers into Sunday's final as King clocked a new American record of 29.60sec, with Efimova just 0.13sec behind.