photo finish 
noun
A close finish of a race in which the winner is identifiable only from a photograph taken as the competitors cross the line.However, after close scrutiny of the photo finish, the race was awarded to the American....
- USA attacked back and in a photo finish Austria crossed the line a mere eleven hundredth of a second ahead of the Americans.
- Why they'll finish second: They just don't have enough strength in the trenches to overtake the Eagles, although no one would be surprised if the two-horse race ended in a photo finish.