They’ll reach the top first - in seconds (7-2)
I believe the answer is:
'seconds' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for runners-up that I've seen before include "Those who come second" , "Those finishing second" , "Those not quite winning" , "Those placed second" , "Those in second place" .)