Eamon Sullivan overcame yet another knock to his battered body to turn in an impressive performance in the opening session of the grand prix swimming meet in Sydney on Friday.

Sullivan, whose career has been dogged by hip problems, shook off recent illness and a knee problem to comfortably qualify fastest for Friday night's 50m and 100m freestyle finals at Sydney Olympic Park.

Sullivan said enforced rest from a recent bout of the flu may have benefitted him since he produced a stunning 100m swim of 48.52secs at last month's Commonwealth Games trials.

He said after Friday morning's 100m heat, in which he swum 47.92 over the short course ahead of the evening's long course finals, he was feeling upbeat despite his ever-present injury worries.

"I wasn't expecting to swim that well in the 100 but coming off a week of illness last week," Sullivan said.

"... I've had a bit of a niggle in my knee the last day but it's not really affecting how I'm swimming too much, it's just a bit of an inflammation or something.

"I'm really excited, I think I've felt more motivated and excited about this year than I have in swimming in general than I have for the last two years so if the body can hold up I definitely think there's got to be some good times to come."

Jessicah Schipper (1:00.56) qualified fastest for the 100m butterfly final after she lost her national title to Stephanie Rice at the trials. Rice (1:01.16) was fifth fastest.

Visiting Swedish world record holder Therese Alshammar, Leisel Jones and Brenton Rickard were among the other heat winners.

The two-day meet at Sydney Olympic Park follows the Australian team's four-day training camp in Canberra and is part of the preparations for the Pan Pacs and Commonwealth Games.

AAP