Dutch distance runner Sifan Hassan kept alive her hopes of an unprecedented Olympic treble after picking herself up following a fall to win her 1500 metres heat on Monday.

The 28-year-old 1500 and 10,000m world champion crashed to the ground when Kenya's Edinah Jebitok tripped and fell in front of her as the bell went for the final lap.

There were gasps of disbelief from within the sparsely populated stadium as it appeared her hopes of a three-pronged attack on the 1500m, 5,000m and 10,000m had disappeared.

However, the Ethiopia-born athlete got back to her feet and moved through the gears as she hunted the leaders down.

Needing to finish in the first six to qualify automatically for the semi-finals, she ate up the ground to the leading pack and had the strength to cross the line in first place in a time of 4min 5.17sec.

She earned herself a round of applause from watching athletes including American Cory McGee, who had run in the previous heat.

"That was awesome," said McGee, who qualified as one of the six fastest losers. "To be able to get up and focus like that and finish first is amazing."

Jebitok, 19, said she was "devastated" after she trailed in 12th in her heat but she was subsequently reinstated and will be in Wednesday's semi-finals.

Her compatriot Faith Kipyegon is likely to be Hassan's greatest threat after she coasted to victory in her heat in a time of 4:01.40.

"I am very happy with my performance," said the 27-year-old. "I will not be focusing on Sifan. I will be concentrating on my own race if hopefully we meet in the final."