James Magnussen's first foray into the contentious Enhanced Games has ended in disappointment, with the doped-up Australian Olympian finishing last in the men's 100-metre and 50m freestyle.

Incredibly, the Olympic silver medallist was well beaten in the 100m by American Hunter Armstrong, who entered the event as a "non-enhanced athlete".

Magnussen was also last in the four-man field for the 50m, all of whom were doping, finishing in 21.52 seconds, which is shy of his personal best of 20.98 set 13 years ago.

"Enhanced" Greek swimmer Kristian Gkolomeev won both finals, going 0.07 of a second faster than Australian Cameron McEvoy's legitimate 50m world record of 20.88.

He pocketed US$1 million for the record, the only record of the meet in the final event in the pool.

"We arrived in mainstream culture; we are here to stay," Games CEO Max Martin said.

Earlier, Gkolomeev missed the 100m world record by 0.2 of a second, with non-enhanced Armstrong second in 48.25 seconds.

Ireland's Shane Ryan trailed in third with 48.92 while Magnussen was last, swimming 49.44, more than 2 seconds slower than his own personal best.

The result will be particularly jarring for the 35-year-old Aussie, who was wearing a garish gold super suit, the sort banned by World Aquatics in 2009, in recognition of him being the first athlete to sign up for the controversial event in February 2024.

Magnussen will likely not be too worried about the time though: even finishing fourth he will pocket $US50,000 ($A70,000).

He will also swim the 50m freestyle at the event.

Athletes can claim a $US1 million bonus for breaking the existing world record at the inaugural Enhanced Games, which are taking place in a purpose-built arena in Las Vegas.

The swimming is taking place in a 50m, four-lane pool.

The concept of the Enhanced Games is that athletes can take performance-enhancing drugs including testosterone, EPO and human growth hormone.

Track and field sprinting and weightlifting are also taking place.

The International Olympic Committee and World Anti-Doping Agency have called the concept a dangerous "betrayal" of sports integrity.