Dutchwoman Sifan Hassan progressed on Wednesday to the second of what she hopes will be three finals but the newly-crowned Olympic Games 5000 metres champion is likely to have to work much harder in the 1500m to beat defending champion Faith Kipyegon.
Hassan, world champion at 1500m and 10000m, is hoping to add those Olympic titles to complete an unprecedented hat-trick. Having been tripped in her 1500m heat on Monday she stayed well out of danger at the back of the second semi-final until the bell.
She then tore home -- seemingly unconcerned about saving anything for the tests still to come -- running hard through the line in a time of 4:00.23 minutes.
Also looking strong behind her was Briton Laura Muir who posted 4:00.73 after opting to miss the 800m to pour all her energy into the metric mile.
Their biggest rival in the final is likely to be Kipyegon.
The Kenyan stretched the first semi-final to come home in a remarkable 3:56.80 -- a time better than the lifetime bests of all but four of the other 25 semi-finalists.
Ethiopia's Freweyni Gebreezibeher and Gabriela Debues-Stafford of Canada look to be the only others with a realistic medal chance but Australian Jessica Hall set a continental record and Nozomi Tanaka a Japanese record as they both went under four minutes for the first time.
Kenyan Winny Chebet, also an outside medal hope, tripped and fell in the first semi-final before finishing last.