Two consecutive participles in a clause

[KSSEEJ]

Dear Sir/Madam

I got difficulties in understanding the structure of the first clause of the following sentence.

"With 73 candidates to be elected unopposed, some 854 candidates will be competing for 339 seats, making the race more competitive." (Quoted from SCMP, HK)

Why there can be two consecutive participles in a clause. To my knowledge, the first participle "elected" is a passive verb and it can 't be followed by another passive verb "unopposed" and thus the clause makes no sense unless
" unopposed" is changed to an adverb form. Would anyone explain it to me ?

Thanks so much.

[5jj]

'Unopposed' is being used as an adjective.