Belfast Newsletter
The Dublin rider finished as the runner-up in the first leg behind Gerard Kinghan, with Alistair Kirk third and Stephen Thompson fourth.
However, Sheils – riding the BikeBitsNI Kawasaki – scored a decisive win in the second leg to clinch the title with 45 points as he won the race from Kirk and Thompson, with race one winner Kinghan fourth.
In the final Enkalon standings, Kinghan took second overall behind Sheils with Kirk third.
Sheils previously won the Enkalon silverware in 2004 and lifted the trophy for the second time in 2013.
In the Supersport class, William Dunlop won both races on the CD Racing/Ivan Curran Racing Yamaha.
Dunlop, who qualified on pole, beat Jamie Patterson and Robert English in race one and led all the way in the second race to take the honours from Robert Kennedy with Patterson third.