World champion James Magnussen said it would take one of the year`s fastest times to win the Pan Pacific Championships 100m freestyle after American stars Michael Phelps and Nathan Adrian threw down the gauntlet Friday.
Adrian, who nudged out Magnussen by one-hundredth of a second to win the Olympic 100m gold in London, topped Friday`s qualifiers with 48.05 seconds.
Australia`s two-time world champion was just 0.2sec behind, with Olympic great Phelps surging into contention on the back of 48.45, just four-hundredths of a second ahead of another Australian, Cameron McEvoy.
Phelps, four months into his comeback from retirement, produced a sizzling swim to ensure he would be the second American in Friday`s final ahead of team-mates Anthony Ervin and Jimmy Feigen.
Magnussen, who has been troubled by a degenerative back condition, was relishing the twin US threat.
"It feels fine, I`m happy to race anybody on my day so I`ll look forward to the challenge," he said.
"It will take a 47 (seconds) to win it, so I think there will be a few of us under that 48-sec barrier."
Only Magnussen and McEvoy have gone under 47 seconds this year, with Brazilian Cesar Cielo holding the world record at 46.91sec.
Phelps, 29, the 18-time Olympic gold medallist, looks to be returning to form after failing to win at this month`s US Championships.
"(Coach) Bob Bowman and I have been working just on the stroke and today my stroke actually felt easier than it normally had," Phelps said.
"The first 50 felt really good and I knew I had to win that heat if I wanted a chance to swim in the final tonight. I actually hit the turn which is a good thing."
Adrian said the quality of the field ensured no risks could be taken chasing a spot in the final.
"The field was like a men`s team meeting in the ready room and the depth we have is just incredible, it`s kind of like the US nationals," he said.
"The times (at the nationals) those guys put up weren`t equal to the quality of swimmers that they were, so you couldn`t risk anything today."Australia`s world champion Cate Campbell was imperious in cruising to the fastest time in the women`s 100m freestyle heats.
The newly crowned Commonwealth Games champion powered to a meet record and the year`s best time of 52.62sec in coasting to victory, 0.88sec ahead of her sister Bronte with American star Missy Franklin clocking 53.65sec.
Campbell said she was not reacting to Sweden`s Sarah Sjostrom`s time of 52.67sec in winning the European crown in Berlin this week.
"That`s my fastest time since the (2013) worlds where I was in the form of my life so to be able to come out and do that I`m very happy," she said.
"I don`t keep track of other people, I don`t think it`s healthy to rate yourself off other people. I can only be as good as I can be.
"I`m sure Sarah and I will have some great head-to-head battles in the years to come."
Franklin was looking forward to an easier day after suffering a back spasm leading into the Gold Coast meet.
"I`m pretty happy with that time, it`s really close to where I was at in the prelims at the nationals," Franklin said.
American Kevin Cordes was the fastest qualifier in 59.70sec for the men`s 100m breaststroke final, with Japanese teenager Kananko Watanabe shading American Jessica Hardy as quickest in the women`s equivalent.
Japanese pair Kosuke Hagino and Daiya Seto topped the men`s 400m individual medley heats, while Americans Elizabeth Beisel and Maya Dirado were fastest into the women`s 400m medley final.