British fencer Corinna Lawrence advanced to the last 32 of the women's epee with a 15-12 victory over Chilean Caterin Bravo Aranguiz at the ExCeL.
At 22 Plymouth-born Lawrence was 14 years younger than her opponent, but more importantly ranked 23 places higher at 43rd in the world.
That showed when the pressure was on at 11-10 with less than a minute left, but she will probably need to be at her absolute best in the second round to have a chance against Romanian world number four Simona Gherman.
A delighted Lawrence said: "I was really nervous at the start - phenomenally nervous - but the crowd were really supportive and helped me a lot. They gave me a lot of confidence in myself. I heard myself screaming and there were 8,000 people screaming too. It was by far the best atmosphere I've ever been in.
"I felt I fought good and bad in places. I think it was just nerves, but I'm thinking about the next fight now, not the last one. I thought it was a bit strange being in the only fight walking out, but I think it was better because everybody was behind me."
Lawrence, whose older sisters Anneka and Rhiannon are both fencing internationals and whose younger brother Kristian competes at youth level, led 4-3 after a very cagey first three minutes.
On the restart it was 90 seconds before the next point was won by the South American, but Lawrence responded to that with three hits in the next 39 seconds - all accompanied by a squeal of delight and fist pump.
She went into the final period 9-5 ahead and kept her nerve when Bravo Aranguiz, whose husband coaches the Chilean taekwondo team, put her under pressure in the closing stages.
Her appearance came after two disappointing days for Britain's 10-strong squad.
Their only win in the opening women's foil came when Natalia Sheppard overcame team-mate Sophie Troiano and then James Honeybone suffered a first-round defeat in the men's sabre. Top medal hope Richard Kruse fights in the men's foil on Tuesday along with James Davis and Husayn Rosowsky.