Chinnor rounded off the season with an impressive 52-14 victory over Clifton on Saturday.
The solid win for the second-placed side in National League 2 South means they finish the season on 131 points and will now contest a play-off place with North runners-up Segley Park.
Elsewhere, Henley Hawks end the season in ninth on 73 points despite a 51-0 thrashing at the hands of third place Redingensians Rams.
In the South West 1 East, bottom club Bicester were joined by fellow Oxfordshire side Grove in relegation to the Southern Counties North.
But Grove finally gave their fans something to cheer with a 34-0 win over Old Centralians after a run of eight consecutive defeats.
At the other end of the table, Oxford Harlquins end the season fourth on 76 points, while Banbury’s 42-31 play-off defeat against Exeter University means they miss out on promotion to the fifth tier.
In the Berks Bucks & Oxon Premier, a dominant Wheatley sealed victory in their final game of the season beating Tadley 11-10. Already promoted second placed Littlemore ended their two-year unbeaten home record losing 19-17 to champions Slough, while Didcot and relegated Abingdon’s seasons ended on April 21 and 14 respectively.