Queanbeyan secured the outright victory they needed to stay in the finals hunt, but didn't count on a brilliant 5-0 spell from North Canberra Gungahlin captain Louis Rutzou to end their season.
Rutzou's incredible five-wicket haul on Saturday was crucial in the race for fourth place on the Douglas Cup ladder as Norths snuck in on a superior quotient.
Both teams finished on 24 points, but Norths with a quotient of 1.28 did just enough to edge out Queanbeyan (1.04) and book a semi-final date with minor premiers Wests/UC.
Weston Creek Molonglo will host Eastlake in the other semi-final from March 12-14.
Norths conceded first innings points last week when they were bowled out for just 131 with Eastlake reaching 5-132 at stumps.
But Rutzou then went to town as Eastlake were dismissed for 133 before Norths showed strong form with the bat behind a half century from Brock Winkler to finish at 3-162.
"It's been a fair few years since first-grade made the finals, so we're ready for the challenge coming up and ready to do well next week," Winkler said.
"We didn't play to our expectations last week, but we came out today all guns blazing and Louis Rutzou just did magnificently and we took that momentum into our batting.
"It was a little bit disappointing we didn't do this last week to confirm our spot, but we played well in the second innings."
The Eastlake lower order had no answer for Rutzou, with the last four batsmen all going for a duck.
"I don't know what happened, it was fantastic to watch from first slip," Winkler said. "I got one to come to me and from there we started to roll.
"Louis just bowled great areas and we took all the chances that came to us. It was a really good seven or eight overs of bowling from him and Hayden Page, who created pressure at the other end."
The challenge doesn't get any easier for Norths as they prepare to take on Wests/UC.
"Everyone in the competition knows what Wests/UC are capable of," Winkler said. "They have a terrific bowling line-up and more than enough great batsmen.
"We have to work extremely hard to do what we did for three days and we're going to try and make an impact."
Wests/UC will be keen to bounce back after a long day in the field, John Rogers belting 178 as Weston Creek warmed up for the finals with an easy victory.
Queanbeyan beat Ginninderra by five wickets and Tuggeranong defeated ANU by 158 runs on the first innings to finish on a high.
Douglas Cup: Eastlake bt North Canberra Gungahlin at Kingston Oval. Weston Creek Molonglo 8-403 bt Wests/UC 186 at Stirling Oval. Queanbeyan 6-157 (dec) and 5-124 bt Ginninderra 86 and 193 at Kippax Oval. Tuggeranong 348 bt ANU 190 at Chisholm Oval.
Semi-finals: Wests/UC v North Canberra Gungahlin at Jamison Oval. Weston Creek Molonglo v Eastlake at Stirling Oval from March 12-14.