Kipyegon cemented her status as one of the all-time great middle-distance runners, becoming the first athlete to claim three successive Olympic 1,500m titles.
Her winning time of three minutes 51.29 seconds broke the Olympic record, and she collapsed to the track, hands on her head in disbelief, after crossing the finish line.
Australia's Jessica Hull took silver and Britain's Georgia Bell bronze as both found the strength to pass Ethiopia's Diribe Welteji on the home straight. Hull clocked 3:52.56 and Bell crossed in 3:52.61, a national record and four seconds quicker than her previous best time.
Kipyegon, who broke her own world record a month ago, spent much of the race in second place on the shoulder of Ethiopia's Gudaf Tsegay, but powered to the front with a lap to go and built an untouchable lead.
Tsegay, world champion over 10,000m, faded suddenly and fell back to cross the line last.
