Olympic and world champion Marileidy Paulino extended her unbeaten streak by winning the women's 400m at the first day of the Diamond League finals in Brussels on Friday.

Paulino, of the Dominican Republic, timed 49.45 seconds for the victory and is unbeaten in one-lap competition since last year's Diamond League meet in Silesia, Poland.

Her winning time, however, was bettered by Sydney McLaughlin-Levrone in an invitational race.

The American, who improved her own world record when winning back-to-back Olympic 400m hurdles golds in Paris, had not competed at a Diamond League event this season and was therefore ineligible for the finals.

But organisers managed to lure McLaughlin-Levrone, who won a second Olympic gold in Paris with the US 4x400m relay team, to Belgium to race in invitational 200 and 400m flat races as a way to "honour" her Olympic achievements.

She touched down in Belgium with the fourth fastest time of the year in the 400m, having run 48.75sec in New York in June.

But she failed to improve that personal best, clocking 49.11sec for a facile victory over a weak field.

"My season always revolves around the major championships, and I put together my programme with my coach Bob Kersee based on those," McLaughlin-Levrone had explained of her absence from European meets.

"Additionally, I already have to be in top form at the US trials to be allowed to go to the Olympics at all. So, attending meetings in Europe in between is not obvious, transcontinental trips are quite tiring."

McLaughlin-Levrone, however, hinted that next year might be different given the world championships will be held in Tokyo in mid-September.

"Perhaps that will open up more opportunities to run in Europe, but we'll see,” she said.

McLaughlin-Levrone's invitational 200m will be held at 1753 GMT on Saturday, 20 minutes before the Diamond League final proper.