The younger Johnson came out on top of the elder Johnson in League One's father-son managerial duel as Lee Johnson's Oldham Athletic defeated dad Gary's Yeovil Town at Boundary Park.
A header from Matt Smith, who starred for the Latics in their FA Cup battles with Liverpool and Everton this season, proved to be decisive and also condemned Oldham's fellow strugglers Portsmouth and Hartlepool United to relegation to League Two.
Following the result, the Glovers find themselves in 5th place as they remain on course for the end-of-season Play-Offs and their final league position will determine who they face in the semi-finals.
The fixture was the first father versus son managerial meeting since 1971 when Bill Dodgin's Bristol Rovers faced Bill Dodgin junior's Fulham.
