Adam Peaty provided plenty of reason to be optimistic on a night of near misses for Great Britain's swimmers at the Olympic Aquatics Centre.

Peaty bettered his own 100 metres breaststroke world record in Saturday afternoon's heats, clocking 57.55 seconds.

And he was just seven one-hundredths of a second slower in clocking 57.62secs in his semi-final, more than a second clear of the rest of the field.

If all and sundry are anticipating ecstasy for Peaty on Sunday, there was agony for Hannah Miley.

The 26-year-old from Aberdeenshire, in her third Games, was overhauled in the final 25m of the 400m individual medley and finished fourth, 0.15secs off the podium. Aimee Willmott was seventh.

Max Litchfield was fourth in the corresponding men's event, while James Guy was sixth in the men's 400m freestyle.

Britain won just three medals, none of which were gold, in home waters at London 2012, but there was optimism of an improved showing in Brazil.

And much of the expectation falls on Peaty, who appears a good bet to end a 28-year wait for glory.

Not since Adrian Moorhouse in Seoul, also in the 100m breaststroke, has a British male won Olympic gold.

But Peaty appears unfazed by the pressure and expectation, merely enhancing his credentials as the favourite on Saturday's opening day of the Games.

Ross Murdoch was sixth in his semi-final in one minute 00.05secs, missing out on a place in the final, finishing 11th overall.

Peaty is already world, European and Commonwealth champion and the gold appears his to lose.

His nearest challenger is USA's Cody Miller, who qualified for the final 1.43secs behind the Briton.

Defending Olympic champion Cameron van der Burgh of South Africa was 0.16s further back in advancing third fastest.

"I think I've got the top three or four times in the world ever now, so it's great," Uttoxeter swimmer Peaty said.

"Tomorrow night's all about just enjoying my first Olympic final and getting out there.

"A lot of people put pressure on it. I don't really feel that pressure.

"I'm in that spot where I've got a real opportunity to do something.

"I'm not going to take that for granted, I know those guys will step up as well."

Murdoch, the European champion over 200m, was frustrated with his own display.

The Balloch swimmer said: "I'm angry at myself - 60.05 is not very good at all. I don't have any answers."

Guy will hope for a strong showing in the men's 200m freestyle, the heats and semi-finals of which take place on Sunday.

The 20-year-old from Bury qualified in sixth place for the 400m freestyle final and went out hard to try to set the pace.

But Guy, who won world silver behind Sun Yang in 2015, faded as Australia's Mack Horton won gold in three minutes 41.55 seconds.

China's Sun, the London 2012 champion, was second in 3mins 41.68secs and Gabriele Dettie of Italy third in 3:43.49.

Guy, who finished almost a second outside his personal best in 3:44.68, will hope to do better in the 200m. He is world champion over four lengths.

"After 200 I felt mint," Guy said. "Then it hit me at 250. The speed's there, the endurance is there, just didn't have that back-end speed today.

"The thing I realised today is that the World Championships is like halfway and the Olympics everyone steps up. That's what everyone did today."

There was little doubt on the destination for the gold in the 400m individual medley as Katinka Hosszu of Hungary won in a world record of 4:26.36. It was the day's second world record after Peaty's.

USA's Maya Dirado took silver in 4:31.15 and Spain's Mireia Belmonte Garcia denied Miley, whose 4:32.54 was just outside her personal best.

The devastated Scot leant her head on the timing pads before congratulating Hosszu on beating the mark Ye Shiwen of China set en route to London 2012 gold.

"It's really hard to know that you were so close to a medal," Miley said. "I could see her coming back at me and I was willing myself to grow an extra two inches as well.

"It's bittersweet. Really happy with the performance, it's the best I've been all year, but it's not good enough for the podium."

Earlier Japan's Kosuke Hagino ended the USA's winning streak, dating back to Atlanta 1996, in the 400m individual medley.

Hagino won in 4:06.05 as USA's Chase Kalisz had to settle for silver in 4:06.75.

Japans' Daiya Seto was third in 4:09.71 and Litchfield fourth in 4:11.62.