One of the most anticipated comebacks in Australian sport- and world swimming- has finally got off the blocks with a tapered Ian Thorpe having an impressive start at the Olympic swimming trials in Adelaide.

He was equal fifth fastest from Friday morning’s heats in front a boisterous crowd in the 200m freestyle, with a seemingly effortless one minute and 49.16 seconds in his heat.

The five-time Olympic gold medallist and former world record holder led for most of the race and in the final lap shut down totally, finishing equal second with David McKeon and behind Ryan Napoleon, who was the fastest qualifier with 1:48.27.

"I'm very happy with the swim," Thorpe said after the race.

"It was a pretty decent time and I'm happy with that time this morning."

Thorpe's teammate and fellow medallist in Sydney 2000 Geoff Huegill tweeted after the race, "Watching #Ianthorpe swimming today was like watching him swim in 2000. Welcome back mate!"

Maybe he was foxing about not foxing? The true test will come when backing up tonight in the semi-finals but the signs are very encouraging.

After fulfilling their nomination requirements last night in the 400m freestyle, McKeon and Napoleon kicked hard to the wall while Thorpe pulled himself effortlessly without bothering to kick.

It was the quickest time of Thorpe's comeback, improving considerably on his 1:50.79 at the Victorian state championships in June. He looked to have several seconds in reserve which is a very positive sign for his quest to make a third Olympic Team.

Thorpe, 29, is swimming in his first national titles in six years. He will need to record one of the top eight fastest times in Friday night's semi-finals to progress to Saturday night's final.

There he requires a top-two finish to book an individual 200m berth in London or top six to be considered as a relay swimmer.

Check out Ian Thorpe Fact Box>>>

Kyle Richardson (1:48.57) was the second-fastest qualifier into the semi-finals, ahead of Kenrick Monk (1:48.72) and Cameron McEvoy (1:48.89).

Pre-race favourite Thomas Fraser-Holmes qualified eighth fastest in 1:49.22.

Earlier, Belinda Hocking led the way into Friday night's 100m backstroke semi-finals after clocking 59.89, the second-fastest time in the world this year.

Top-ranked Emily Seebohm was second in 1:00.90.

"It's not the hardest swim I have ever done but there are still semis and finals so I obviously saved some in the tank," Seebohm said.

Leiston Pickett (1:06.92) and Sarah Katsoulis (1:08.12) led the way into the 100m breaststroke semi-finals ahead of Olympic champion Leisel Jones (1:08.33).

Defending champion Kylie Palmer qualified fastest for Friday night's 400m freestyle final in 4:09.21.

Remy Fairweather, 14, was second in 4:10.28 and Bronte Barratt third (4:10.63).

Palmer and Barratt again look set to fight out the final after Palmer scored a narrow victory at last year's titles.

Ben Treffers (54.59) led the way into the 100m backstroke semi-finals ahead of Josh Beaver (55.46) and Matson Lawson (55.94).

One of the pre-race favourites Ashley Delaney (56.88) was 18th fastest but also went through thanks to two scratchings.

Geoff Huegill will not swim in Friday night's 50m butterfly final, opting to pull out of the non-Olympic event ahead of the 100m, which starts on Tuesday.

AOC and AAP