Geddington started well, but then collapsed from 96 for three to 171 all out, with Northants youngster Amrit Basra leading the way with three for 33.
There were also two wickets apiece for Niall Malin and Paul Harris, while Andrew Reynoldson hit 64 for the home side.
That target was never going to be an issue for ONs, and they coasted to 174 for two in just 28 overs thanks to 61 from Rob White, 43 from Basra and 33 not out from skipper Thomas Hafil.
Horton House went down by seven wickets to Brigstock, having at one point looking odds-on to claim an opening day win.
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Horton totalled 234 all out in 46 overs, and they were indebted to 79 not out from William Knibbs as they recovered from 72 for six, with Harry Dube adding 44.
D Muhammed claimed four for 31 for Brigstock, and then played a key role with the bat as well.
Mark Wolstenholme then raced in to take four for 67 as Brigstock slumped to 140 for seven in reply, but Muhammed hit an unbeaten 59 and Bashrat Hussain 27 not out to see their side home with an unbroken 96-run partnership.
Earlier, opener George Groenland had held the innings together with 70.
The clash between Overstone Park and Brixworth ended in an exciting draw.
Overstone batted first and made a useful 248 for six in their 50 overs, with Charles Edwards hitting 65, Kunal Patel 47 and Jordan Capel 38.
For Brixworth, Oliver Pearce took three for 28.
A couple of Northants academy players then played starring roles in Brixworth's innings.
Opener Harry Gouldstone batted superbly to hit 100 from 109 balls, but his fellow County youngster James Sales did the damage with the ball, claiming four for 53.
Brixworth were always in touch, with ex-Northants batsman Rob Newton making 40, but they eventually fell short and settled for the draw at 236 for six.
Rushden & Higham were seven-wicket winners over Oundle Town.
Chris Law bagged four for 17 as Oundle were rushed out for just 119, although that was a bonus as they were at one point 83 for nine.
There were also two wickets apiece for Tom Firm and Callum Nicholson.
Rushden lost a couple of early wickets in reply, but then Shiv Patel came in and hammered 73 from just 44 balls to see them home at 121 for three in 19.3 overs.
Finally, reigning champions Peterborough were easy winners over Desborough.
Justin Watson hit 35, Simon Renshaw 32 and Lewis Ward 30 as Desborough posted 192 all out, with Mark Edwards snaring four for 43.
Posh then cruised to 193 for four thanks to an unbeaten 63 from Chris Milner and decent efforts from Josh Smith (42) and David Clarke (32).