SWIMMING:TOMORROW MORNING here, Michael Phelps will be expected to swim to his seventh gold medal of these games when he competes in the 100 metre butterfly final. But last night in the Water Cube he offered just the faintest sign of fallibility.

Phelps was more than one-tenth of a second behind the winning time posted by Serbia's Milorad Cavic and finished second in his heat in that event.

The Baltimore sensation shrugged it off with the crooked grin that has already become the most photographed smile in Olympic history.

But given the way Phelps has been almost nonchalantly shattering records this past week, that swim perhaps offered just the faintest hope for his competitors on Saturday morning that the toll of his phenomenally consistent and unforeseen excellence is exacting its toll on that long, singular frame of his.

He swam the 200 metre medley in the early hours of this morning, and even if, as expected, he took gold number six, that race may further diminish his daunting reserve of energy and strength.

For once, Phelps enjoyed a night of relative civility in the sopping mixed zone through which the athletes file afterwards.

Over the past few mornings, the clamour to speak to Phelps has been reminiscent of that iconic footage taken outside the US embassy during the fall of Saigon, and Phelps has, at times, looked visibly uncomfortable with the desperate attempts of journalists to get within earshot of his words.

Last night, it was like the old days, when he was just a young star on the up in a water world where the name of Ian Thorpe was used as an arbiter of general brilliance.

He smiled in acknowledgement of the suggestion there was something novel - if not outright shocking - in watching him finish behind another swimmer, albeit in a mere heat.

After the first length, Phelps's times left him in joint sixth place. When that statistic was posted on the electronic board, it was enough to cause a faint murmur of apprehension to pass through the crowd, a brief fear that the opportunity to witness Phelps complete his march to sporting immortality would come undone on one of the most mundane tasks he has faced. He did what he has always done, moving up through the gears and defying the law that he should tire in the latter stage of the race and posted the fastest split on the home leg.

"I could see after the first 50 what was happening and I thought, okay, this is going pretty fast," he explained.

"I think my first 50, I need to be closer than a body length behind. It felt fine. I was able to come back good and get some rest for the final. I'm gonna get some more rest tonight and get to bed as early as I can. Tomorrow is a big game."

If Cavic or some other unheralded contender were to somehow have the swim of his life and take the medal that has all but been pre-ordained as belonging to Phelps, it is not entirely clear if the feat would be widely celebrated or regarded as some sort of larceny on the dominant athlete in Beijing.

Afterwards, excited Serbians asked Phelps about Cavic's times.

"Cavic has put up good times all year," Phelps said, happy to talk about someone other than himself. "He went to Cal (University of California) and he is a good sprinter. He has been there for the past few years and he is going well."

As Phelps left the arena, Ireland's Melanie Nocher swam and won her heat of the 200 metre backstroke.

Nocher set an Irish record with a time of 2:12.29, but it was not fast enough to gain passage through to the semi-finals.

She had mixed feelings about the evening, pleased that her swim vindicated the decision by Swim Ireland to select her but also somewhat taken aback by the consistently eye-opening times that have been set in the pool all week.

"I couldn't be more pleased," she said. "I was really nervous going into it but I seemed to calm down before we raced and I just remembered to enjoy myself and pushed it in the last 50, especially when it was hurting, and looked up and it was a faster time.

"It is going to take 2:10 to get into the semis so I really can't wait to get back training and do some fast times.

"This time would have got me in at Athens but it is just a whole new kettle of fish now, a really fast pool and a great atmosphere. It is perfect conditions."

Nocher hopes that by the London Olympics she will be ready to make further strides, but she admitted that the whole culture and scale of the Olympics can be a shock to the system of any Irish athlete.

"I don't think you can go into the Olympics and think you are going to go badly. I was really nervous two days ago. It is very tense and competitive here but the Olympics is really what you take away from it.

"I have just been trying to take everything in. Ireland is very young in terms of swimmers and they will learn from European and Commonwealth games.

"But definitely, 2012 is going to shock some of them and it shocked me, and I just can't wait to get back in the gym and training.

"This really gave me a shock, you know, about how fast the world is getting. I am getting older and I need to train harder and make my mark a bit more."

Nocher's exit ended Irish involvement in the pool, but, like the rest of the world, she will be watching to see if Phelps can complete the haul of eight medals in Sunday morning's race - the 100m medley relay - that will define competitive swimming in the modern era.