American Allyson Felix was made to fight all the way before winning the 400 metres in tonight's first Diamond League meeting of the season in Doha.
Felix made a quick start and looked in control of the race before Botswana's Amantle Montsho surged onto the triple world 200m champion's shoulder around halfway.
However, Felix was able to respond and held on at the line to record a world-leading time of 50.33 seconds, with Montsho just 0.08secs behind.
Felix, who won 21 of her 22 races last year, has yet to decide whether she will double up over 200 and 400m at this year's World Championships in Daegu, but admitted: ‘It's definitely something I'm considering.’
There was more success for America in the women's 100m hurdles, with Kellie Wells leading a 1-2-3.
Wells equalled her personal best with victory in 12.58s ahead of Danielle Carruthers and world indoor champion Lolo Jones.
American Walter Dix also won the 200m in 20.06s, despite appearing to step outside his lane on more than one occasion.
Britain's Michael Rimmer produced an impressive performance to finish second in the 800m to Kenya's Asbel Kiprop.
Kiprop is the Olympic champion over 1,500m and used his strength well, following the pacemaker until the bell and then leading all the way to the line.
The 21-year-old clocked 1:44.74, with European silver medallist Rimmer finishing in 1:45.12.
Yenew Alamirew gave a noisy Ethiopian contingent in the crowd plenty to cheer with victory in the 3,000m, the 20-year-old's time of 7:27.26 making him the ninth fastest of all time over the distance.
In the field events, France's Teddy Tamgho easily won the triple jump with a best of 17.49m in the second round, 40cm clear of Leevan Sands of the Bahamas in second.
And 19-year-old local Mutaz Essa Barshim demonstrated his enormous potential by equalling his personal best of 2.31m in finishing third in a high jump competition won by American Jesse Williams at 2.33m.
