Double Olympic champion Rebecca Adlington will need to dig deep into all her talent and experience if she is to come near to replicating her bronze medal of two years ago after she scraped into the 400metres freestyle final on the first day of action at the World Championships in Shanghai.
The 22-year-old finished third in her heat, and seventh overall, in four minutes 07.38 seconds but she looked a shadow of the swimmer who has impressed this season.
In contrast, defending champion Federica Pellegrini looked awesome as she set the fastest time, 2.62secs ahead of the Briton in 4:04.76, and her fresh face and knowing half-smile at the end of her heat indicated her confidence and the knowledge she clearly has plenty left for tonight.
Also impressive were Frenchwoman Camille Muffat and Lauren Boyle of New Zealand, who led from start to finish in Adlington's heat.
Lotte Friis, defending 800m freestyle champion, also had a superb start to the week when, after impressing over eight lengths, she returned to help Denmark into the final of the 4x100m freestyle - ahead of Great Britain - in her first outing in that relay.
It was a disappointing 400m freestyle with Jazmin Carlin 15th in 4:09.64 although it emerged she had contracted glandular fever in March which had severely hampered her preparations.
Tonight's final will see Adlington start in an outside lane although it must be remembered this is where she swam at the last World Championships in Rome where she clinched a bronze medal.
She said: "That didn't feel great but I am happy I am in the final.
"Now I'm going to rest up and see what I can do tonight."
A tearful Carlin declined to speak.
There are four finals at the Oriental Sports Centre tonight and, apart from Adlington, the men's 4x100m freestyle relay are the only other British representatives.
Neither David Carry nor Robbie Renwick made it through in the men's 400m freestyle, coming in 15th and 18th respectively.
It promises to be a fascinating, and fast, race with Sun Yang leading the field ahead of American Peter Vanderkaay and defending champion Paul Biedermann, who took down Ian Thorpe's world record in Rome two years ago.
The men's sprint freestyle relay qualified for tonight's final in eighth spot, edging out a Brazil squad that would have included Cesar Cielo, free to swim after the Court of Arbitration of Sport upheld his warning rather than imposing a ban after a positive drugs test.
The quartet of Adam Brown, backstroke specialist Liam Tancock, Grant Turner and Simon Burnett scraped through in 3:15.35.
Tancock, who swam the fastest split of 48.51, said: "Pretty good, starting off the World Championships, part of the team here and it seemed to go pretty well."
Burnett, like Brown, is based in the United States and he added: "Training in the States is a great bonus because you get to race against these people.
"It's not just the Americans you race against, it's a lot of other foreign swimmers, and it gives you that exposure and really sharpens you up for events like this and relays especially."
The event is the last on the programme and will feature Michael Phelps going for his first gold medal.
The women were edged out by Denmark, and Friis, in 3:39.74.
Fran Halsall, silver medal winner in the individual event in Rome, had a superb leg, swimming 53.35, the third fastest split in the race.
She was not too downhearted, saying: "I think we did a good turn, 3:39 is nearly one of our best times.
"It hurts not to be in the final but I think it will spur us on.
"We're a group of toughies."
Elsewhere, Jemma Lowe was impressive as she qualified third fastest for tonight's 100m butterfly semis with Ellen Gandy in seventh.
Hannah Miley and Siobhan-Marie O'Connor reached the last 16 of the 200m individual medley with less than a second covering the top seven.
Antony James qualified 15th for the 50m butterfly semis, with Cielo leading the field after a heat that placed him in the lane next to Roland Schoeman, the former world record holder who was scathing of CAS' decision on the Brazilian.
Michael Jamieson scraped into the 100m breaststroke semis in 15th but Kris Gilchrist missed out in 26th.