Daniel Ryder scored the winning goal with 7:38 left as the Petes downed the 67's 2-1 in OHL action last night in Peterborough.
It was the final regular-season meeting between the clubs, which will likely face each other in the first round of the playoffs starting later this month.
The Petes won 6-of-8 games between the teams, including all four meetings in Peterborough.
Ryder's shot through traffic during a power play decided last night's contest.
In contrast, Ottawa went scoreless on 12 power-play chances as its record fell to 26-30-5-2.
The Petes (45-14-2-2) scored short-handed early in the first period when Jamie Tardif beat goaltender Danny Battochio. The 67's tied it later in the period on Julian Talbot's 28th goal of the season.
The 67's return home tonight to play the Brampton Battalion at the Civic Centre (7:30 p.m.).
Ottawa will also be playing Sunday when the Barrie Colts come to town (2 p.m.).
The 67's then play the Frontenacs in Kingston on Tuesday, followed by home games vs. Oshawa on March 17 and Sudbury on March 19.
In QMJHL action tonight, the Gatineau Olympiques play host to Rouyn-Noranda at the Robert Guertin Centre.