Dutch runner Sifan Hassan stayed on course for a historic Olympic treble with a brilliant victory in the 5,000m on Monday as sprint hurdler Jasmine Camacho-Quinn claimed a first track and field gold for Puerto Rico.
Ethiopia-born Hassan put on a masterclass in distance running to claim gold, surging clear of the field with around 250 metres to go in a time of 14min 36.79sec. Kenya's Hellen Obiri took silver while Ethiopia's Gudaf Tsegay collected bronze.
The win means Hassan's dreams of claiming three gold medals in Tokyo -- the 1,500m, 5,000m and 10,000m -- remain very much alive.
Monday night's stirring 5,000m victory capped a remarkable day for Hassan, who only 12 hours before had produced an improbable comeback to advance from her opening 1,500m heat.
Hassan's treble hopes looked to be in jeopardy after she dramatically tumbled to the track after a heavy collision at the start of the last lap.
But she picked herself up and produced a devastating turn of speed over the final 350 metres to finish first and advance.
"It has been an amazing day," said Hassan after her 5,000m win. "When I fell down and had to jump up I felt like I was using so much energy.
"I can't believe it. I used all my energy this morning and I was kind of tired. I felt terrible afterwards and I never thought I am going to be Olympic champion."
Hassan's victory was one of five gold medals decided on day four of the Olympic track and field competition.
- Puerto Rico upset -
In the women's 100m hurdles, Puerto Rico celebrated the country's first ever athletics gold at the Olympics as US-born Camacho-Quinn upset world record holder Keni Harrison to win in 12.37sec.
It completed a fairytale redemption story for Camacho-Quinn, who had exited the 2016 Olympics in tears when she crashed out in the semi-finals after falling at the last hurdle.
"For such a small country it gives little people hope," Camacho-Quinn said. "I wanted to be a gold medallist and I manifested that. I spoke it into existence."
Harrison claimed silver in 12.52sec while Jamaica's Megan Tapper took bronze in 12.55sec.
In the men's long jump, Miltiadis Tentoglou became Greece's first gold medallist in the event after snatching victory from Cuba's Juan Miguel Echevarria with his final leap.
The 23-year-old soared 8.41 metres to equal Echevarria's best mark but the Greek had a superior second-best jump (8.15m to 8.09m).
- Kenyan reign ends -
In the men's 3,000m steeplechase, Morocco's Soufiane el Bakkali ended Kenya's 37-year dominance of the event to take gold in 8:08.90.
Kenyan runners had won every Olympic steeplechase gold medal since the 1984 Olympics. Lamecha Girma of Ethiopia was second in 8:10.38, while Kenya's Benjamin Kigen claimed bronze in 8:11.45.
The women's discus saw the United States bag their first track and field gold of the Tokyo Games with Valarie Allman's throw of 68.98m enough to secure victory.
Germany's Kristin Pudenz took silver with a throw of 66.86 while Cuba's world champion Yaime Perez the bronze.
In other track action on Monday, newly minted 100m champion Elaine Thompson-Herah signalled she is ready to claim the sprint double for a second straight Olympics with a personal best 21.66sec in the 200m semi-finals.
Thompson-Herah looked to have plenty left in the tank as she cruised to victory, suggesting another fast time could be on the cards in Tuesday's final.
Compatriot Shelly-Ann Fraser-Pryce qualified in 22.13sec.
In the men's 400m, defending champion and world record holder Wayde van Niekerk's reign came to an end after the South African could only finish fifth in his semi-final.
The performance of Monday's semis came from Grenada's Kirani James, the 2012 Olympic gold medallist, who looked in terrific form as he won in 43.88sec.
In the women's 400m hurdles semi-finals, American rivals Dalilah Muhammad and Sydney McLaughlin set the stage for another epic showdown, shrugging off treacherous conditions as an hour-long downpour lashed the track to clock the two fastest times of the round.
World record holder McLaughlin made light of the wet track to win her semi in a brisk 53.03sec while Muhammad was fractionally slower in her qualifier to take victory in 53.30sec.