Certainly you can depend on us rising to the top (6)
I believe the answer is:
surely
'certainly' is the definition.
(I know that certainly can be written as surely)
'you can depend on us rising to the top' is the wordplay.
I cannot quite see how this works, but
'you' could be 'u' (commonly used in online communication) and 'u' is found in the answer.
'depend' could be 'rely' (I've seen this before) and 'rely' is present in the answer.
A single letter 's' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for surely that I've seen before include "Indubitably" , "Without doubt, certainly" , "Definitely or positively" , "With certainty" , "it would seem ironic?" .)