But there was heartbreak for 18-year-old welterweight Billy Joe Saunders who was well beaten 13-6 by world-class Cuban Carlos Banteaux and became the second British boxer to exit the competition.

Jeffries had blown a one-point lead with 15 seconds left on the clock to leave the scores locked together at 5-5 and force an examination of the five judges' cards for the total number of scoring punches.

And the 25-year-old could hardly contain his relief at edging the verdict which takes him into the quarter-finals and a clash with Hungary's Imre Szello, whom he beat by a single point in the EU Championships in Poland in June.

Jeffries said: "I've only ever dreamed of winning an Olympic medal since I was six years old, and I'm so close now.

"You never know how the countback score is going to go and I was praying to God to let me win.

"There was a lot of pressure on me because the Olympics is the biggest sporting event going and it has been a long week for me. With the rest of the team doing so well that added to the pressure."

Jeffries conceded his win over Alvarez, twice a Pan-American champion, was a "horrible fight", in which he was never behind but unable to pull into a clear lead in a mauling and forgettable contest.

But he will shut that to the back of his mind ahead of his match against Szello next Tuesday evening, doubtless buoyed by the number of messages of support heading his way from back home.

Jeffries added: "It puts even more pressure on you when you're getting all these messages and you don't want to let anybody down. I've been getting hundreds of them and the support back home has been amazing."