Belvoir is within sight of crashing back into the top six and North in danger of falling out.
North fell for a disappointing 161 from 67.1 overs, with the Eagles 0-30.
“It means our destiny is pretty much up to us, we’re not leaving it to anyone else,” Belvoir’s Zac Simmonds said.
“There’s still a long way to go, but it was as good a day as you probably could have asked for at the start.”
North was fifth (66.79 points), with the Eagles seventh on 63.96.
Belvoir sent North in and the home side was stunned when the competition’s leading run-scorer Ash Borella failed to open, batting at four.
“Yeah, it was a bit strange,” Simmonds admitted.
“He’s an attacking batsman and likes the ball coming on and backs himself in, so it’s always a hard thing for an opening bowler to start against.
“I’d definitely prefer him in the middle order because if he comes off (at opener) and makes a big 50 at a run a ball, like he has a lot in the last few years, it can burn your two-day game in the first hour.”
Ash Hulme posted a patient 40 as opener from 123 balls, while the in-form Brendan Simmons (28), Ryan Addison (28) and Borella (26) chipped in.
Prefer him in the middle order because if he comes off (at opener) and makes a big 50 at a run a ball, like he has a lot in the last few years, it can burn your two-day game.Zac Simmonds
Hulme and Simmons put on 52 for the second wicket, but that was the only half-century stand.
North was 4-137, but then lost 6-24 as the Eagles seized the advantage.
“I think the pleasing thing was that even when they were in that position where it could have gone either way, our bowlers were sticking to their plans, it was still keeping it nice and tight,” Simmonds said.
Off-spinner Simmonds claimed 4-67 from 28 overs, while Cameron McCormack snared 3-28 from 14.
Drew Cameron grabbed three catches, including two blinders in slips.
“One was diving to his left to get Ash (Borella), while the other was a cut from (Ash) Hulme,” Simmonds said.
“It was going pretty quick, he stuck his hand out and was able to knock the ball up in the air and catch it.”
John Spencer (15) and import Jack Jessop (12) will resume on day two.
Belvoir is clearly favourite, but North’s attack showed its fighting ability by restricting Tallangatta to just 90 to snare a crucial win in the last round.
Greg Daniel was the key to that win and he could well hold North’s finals hopes in his right hand as the club faces a brutal last round against Wodonga.
Daniel has taken 30 wickets at 16.8.
The former Victoria Country representative scored a painstaking 12 from 72 balls, so he too will work on the theory he’ll be able to strangle Belvoir’s batting.
But if the Eagles do win, they should cement a top six finish against eighth-placed St Patrick’s in the final round.