Resilient superstar Grant Hackett resumed normal service by winning the 800m freestyle but not before being thoroughly tested again by Craig Stevens.

The three-time world champion in the event only pulled away from Stevens after the 650m mark at the national titles in Brisbane to win in seven minutes 48.54 seconds.

It looked like Stevens (7:50.71) had forgotten his place in the swimming pecking order as the pair produced the two quickest 800m swims in the world this year.

There has been plenty of speculation surrounding Hackett's health after the big man pulled out of Tuesday night's 200m freestyle final in a bid to freshen up for the rest of the meet.

The 26-year-old won the 400m freestyle on Sunday night but his time was sluggish by his high standards and his camp said his taper was off.

He demonstrated again his mental toughness to drive off Stevens who is in the best form of his colourful career.

"In a ten year swimming career you are going to have ups and downs, this is definitely a down," Hackett said of his taxing week.

In terms of finding form, he said: "I am not there yet."

However he felt he found more rhythm as the race wore on, but his time was still some ten seconds outside his world record.

Stevens, who pushed Hackett all the way in the opening night in the 400m, paid tribute to the victor.

"He is a champion. When athletes like that are down they are always going to come back up, it just shows you how good the guy is," Stevens said.

Hackett's coach Dennis Cotterell said he had not expected "great swims" from his star charge as they tinkered with his programs in a bid to get him back into heavy training straight after the trials.

The Australian team captain now turns his attention to his signature event the 1500m with heats on Saturday.

Meanwhile Bronte Barratt (1:58.07) continued her emergence as a middle distance force by upsetting Linda MacKenzie (1:59.24) and Commonwealth record holder Libby Lenton (1:59.29) in the 200m freestyle.

The 17-year-old Queenslander revealed she discovered she had been suffering from the spinal condition scoliosis just three months ago.

"I kind of knew about it," she said.

"I had some pain in the forearm and shoulder but when I found out I stayed pretty focused, I didn't let it affect me. That makes it more satisfying to come out here and swim like that."

Barratt's time lifted her to the position of Australia's third fastest swimmer in the four-lap event behind only Lenton and 2000 Olympic champion Susie O'Neill.

Backstroker Sophie Edington took the unusual approach of trying to bounce back from her disappointment in the 100m by wearing an itsy bitsy pink bikini in the 50m semi-finals.

It didn't affect her performances too much, she still qualified second fastest behind Tay Zimmer.

World record holder Jess Schipper (2:07.74) led qualifying for Thursday night's 200m butterfly as did Eamon Sullivan (49.11s) for the 100m freestyle final ahead of Ashley Callus (49.49).

West Australian Travis Nederpelt (1:57.45) collected his third straight 200m butterfly national title and Brenton Rickard completed the 50-100m breaststroke double.

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