Lithuania's Ruta Meilutyte became the first 15-year-old Olympic swimming champion in 40 years as she powered to the 100m breaststroke gold medal in London on Monday.

Meilutyte held off fast-finishing American world champion Rebecca Soni to become the youngest winner of an Olympic swimming gold since Australia great Shane Gould enjoyed a triple triumph at the 1972 Munich Games.

The blonde schoolgirl was emotional about her achievement and shed tears on the podium after her country's national anthem was played to sustained applause from the crowd at the Aquatics Centre.

Meilutyte also became the first swimmer to win a gold medal for Lithuania, once part of the former Soviet Union.

"I put all my strength into that race. I still can't believe it. I'm shocked, but in a good way," she said.

"I started crying on the podium, that's when it started to sink in.

"I can't believe it. It's too much for me. It was hard and difficult. But it means a lot to me and I'm so proud."

She surged clear off the starting blocks and led all the way to beat Soni in one minute 05.47 seconds, prevailing by just eight-hundredths of a second. Japan's Satomi Suzuki was third.

Meilutyte, coached in Plymouth, south-west England, arrived at the Games with a best time of 1:07.20 and whittled it down by 1.73secs to become Olympic champion.

Her coach, Jon Rudd, said: "She goes to a British school, swims for a British club and has a British coach. We should feel really proud of her: she is a product of our nation's work."

Soni believes Meilutyte will have a great future in swimming.

"It was definitely a surprise, but after her prelim swim, I knew she would be a great competitor," Soni said.

"It is amazing to be able to do that at 15. She swam three races impressive, so it wasn't out of nowhere.

"It was an honour to have swum with her as she will do great in the future."

The start of the final was delayed by a technical malfunction forcing American Breeja Larson prematurely into the water.

"The start was definitely interesting, we were all put off in the same way, I felt sorry for Breeja, who actually jumped in the water," said Soni. "It is what it is."

Larson at first feared she would be disqualified for a false start.

"I was worried about a DQ (disqualification) at first, I went into the water and my heart sank," she said.

"I got ready for my mark and it was just the swimmer's reaction to go.

"No one else went, I came up and I am glad they didn't keep swimming."

Australia's triple Olympic gold medallist and defending champion Leisel Jones could not last the pace and finished fifth.