The 100 Guineas Cup or Hundred Guinea Cup (£100 Cup) regatta of 1851 was the first competition for the America's Cup trophy. Originally, Cup of One Hundred Sovereigns, the value of the trophy was 100 pounds-sterling, hence its names, variations on 100 Pound Cup. The race was won by the yacht America, leading to the trophy being renamed "America's Cup".

The 1851 competition was the first to compete for the trophy, hence the 1851 America's Cup or 0th America's Cup being zeroth, sequentially preceding the first America's Cup of 1870. The event "The America's Cup" would not be founded until 1857, when the deed of gift established the America's Cup racing regattas. The 1851 edition was a fleet race, unlike modern America's Cups finals, which are currently match races.

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