Some games of tennis get harder (3)

I believe the answer is:

set

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'some games of tennis' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for set that I've seen before include "Mount (gem); scenery" , "Become fixed or solid" , "Gel; group" , "Prescribed" , "Prepared" .)

I've seen this clue in The Irish Independent.

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