Like getting into the last in open group and relaxing (6)
I believe the answer is:
easing
'relaxing' is the definition.
(eg relaxing or easing some pressure)
'like getting into the last in open group' is the wordplay.
'like' becomes 'as'.
'getting into' means one lot of letters goes inside another.
'last' suggests the final letters.
'open' indicates taking the first letters (take the opening letter).
The final letter of 'the' is 'e'.
The initial letter of 'group' is 'g'.
'e'+'in'='ein'
'as' going within 'ein' is 'easin'.
'easin'+'g'='EASING'
'and' acts as a link.
(Other definitions for easing that I've seen before include "Allaying, alleviating" , "falling off?" , "Becoming less severe" , "giving assistance" , "comforting" .)