The Swan Yamaha rider, who has targeted winning all three races of the triple-header weekend, got a flying start from pole position and finished ahead of championship rivals Josh Brookes and Shane Byrne.
Second-placed Brookes (Tyco Suzuki) came in 4.508 seconds behind Hill, with Byrne (Rapid Solicitors Kawasaki) almost six seconds further back down the field.
The podium after Race One is reflected in the championship standings which Hill tops with 184 points, 14 ahead of Brookes and 15 from Byrne.
Michael Laverty (Samsung Honda) had started the race second on the grid, but crashed out on the fourth lap. That saw Brookes and Byrne lose time as they had to take evasive action and Hill opened up a comfortable lead and cruised to victory.
"I really wanted that win and to start the weekend with that was the best possible start after getting the pole position earlier," Hill said after the race. "There are a few areas we need to polish up on but it was a good race and I need to thank the Swan Yamaha team.
"I didn't really know what was happening behind me; I just saw the gap on my board but I just kept my head down and did the job. It was a fantastic race and hopefully we can have more of the same tomorrow."
1. T. Hill - Swan Yamaha
2. J. Brookes - Tyco Suzuki
3. S. Byrne - Rapid Solicitors Kawasaki
4. N. Haga - Swan Yamaha
5. J. Westmoreland - Team WFR Honda
6. T. Bridewell - Supersonic BMW
7. C. Walker - Pr1mo Bournemouth Kawasaki
8. P. Hickman - Buildbase BMW
9. G. Gowland - Team WFR Honda
10. B. Burrell - Buildbase BMW