Roberto Pavoni and Joe Roebuck failed to make it through to the final of the swimming 400 metres individual medley which saw defending champion Michael Phelps only just scrape through on the first morning of Olympic competition.
Pavoni finished 13th with Roebuck 24th although there was almost a huge shock as Phelps only just made it through in eighth while Beijing silver medallist Laszlo Cseh was edged out.
Fastest through was Japanese swimmer Kosuke Hagino while world champion Ryan Lochte recorded the third best time although he was clearly easing down when caught by South Africa's Chad Le Clos.
Roebuck was the first home swimmer in the pool and his appearance behind the blocks was greeted by a huge cheer at the Aquatics Centre. The Rotherham-born swimmer led after the opening butterfly leg but he fell behind on the backstroke, to turn seventh at the halfway point.
The Loughborough ITC athlete then found himself in eighth with 100m to go and could not make any inroads to touch in four minutes 20.24 seconds although a disqualification bumped him up.
Pavoni was alongside Beijing triple silver medallist Cseh and one removed from Phelps. The 21-year-old produced a strong breaststroke leg to find himself in fifth going into the final freestyle 100m.
Fifth at the last turn, he clawed away and managed to touch in fourth in 4:15.56.
Phelps' appearance prompted an ovation as he commenced his final Olympic programme, retirement beckoning after London. First after a commanding butterfly, it was Hungarian Cseh who entered the final freestyle leg first, but the American clawed it back to touch in 4:13.33, ahead by 0.07.
Cseh's failure to progress was a shock and Phelps will breathe a sigh of relief that he edged through. While Phelps has already secured 14-time Olympic titles, it is Lochte whose star has risen over the last couple of years, culminating in five golds in Shanghai last summer.
The Florida-based swimmer won last month's US trials and he looked fearsome this morning. Despite being caught by Le Clos at the touch, the American was clearly easing down to touch in 4:12.35.