The 15-year-old Dunedin swimmer lined up 10m away from American Katie Ledecky in Gwangju, Korea, yesterday.
It was the toughest - and most exciting - challenge the Kavanagh College pupil could have asked for in her Fina World Championships debut.
Not only is Ledecky one of the best female swimmers ever, but she is also the swimmer Fairweather has looked up to.
Fairweather's 400m freestyle time of 4min 12.30sec left her 17th overall, out of 43 swimmers.
Swimming in the fifth and final heat, she raced against many of the fastest finishers.
Ledecky showed her class as she powered away to win both the heat and finish top qualifier in 4min 01.84sec.
That was a time 5sec short of the world record she set at the 2016 Rio Olympics. However, there was a feeling she still had more to come.
The possibility of racing Ledecky had excited Fairweather when she spoke the Otago Daily Times before leaving for the championships.
The draw was then unknown.
Her goal had been to do her best, and she certainly did that.
Swimming on the outside lane, she was third in her heat at the 50m mark.
At that point she trailed Ledecky by about half a second.
While the older swimmers took over as the race went on, Fairweather kicked on to finish eighth in the 10-swimmer heat.
Her next race will be tomorrow's 200m freestyle, in which she has been drawn in the sixth heat.
