Defending champion, Eunice Sum, qualify for Saturday's women 800m finals on a laborious note after going through as one of the fastest losers on Thursday in Beijing.

The Commonwealth champion clocked 1: 57.56 to cross the line third in a photo finish behind winner Canadian, Melissa Bishop who set a national record of 1:57.54 and Marina Arzamasova of Belarus who returned a personal best of 1:57.56.

The result saw Sum suffer is first defeat since August last year at the Sainsbury's IAAF Diamond League meeting in Birmingham ending a run that stretched one year and three days.

Starting in lane five in the third semi, Sum stretched in front after the bell to open the pace in the race that was the fastest of the three qualifiers.

With only the first two finishers and equal number of fastest losers booking their tickets to the final, Sum increased the tempo but she was caught by Britain's Lynsey Sharp at the 200m mark.

The three crossed the bell in 57.31 with Sum still holding on her lead as she tried to push hard from the inside but the rest of the pack led by Netherland's Sifan Hassan stayed right on her shoulder.