Calvert's Kate Brickner was outscoring North Baltimore by herself at halftime.
The Senecas' star had 18 points at the break; Calvert led 34-17.
The Tigers did their best to take Brickner away after that, and for the most part succeeded. Brickner managed just four points after the break.
But behind a solid second half from Nicole Bickley, Calvert persevered, 61-44.
"I took my open shots, and I just happened to be hitting them that time," Brickner said of a first half in which she made five baskets - three 3s. "My teammates fed me the ball; it worked out pretty well.
"They picked up the pressure in the second half, so other people stepped up and scored, and I was happy to see that."
Taylor Ritzler added 12 points for the Senecas, who improved to 5-0, 2-0 in the Midland Athletic League. Bickley scored seven of her nine points after halftime.
Calvert never trailed, scoring the contest's first six points and leading 15-7 at the first stop. The lead grew to 28-15 with 2:43 left in the half after a stickback by Lindsay Bickley, and 32-15 after a Samantha Beckley layup.
The Senecas were aided by their defense, which forced the Tigers into 11 second-quarter turnovers.
"Calvert's one of the best teams in the league," said North Baltimore coach Greg Frost, whose team dropped to 2-4, 0-2. "We were playing on their floor here, it's a tough place to play ... our team is young, it's a learning experience for us there."
North Baltimore was able to climb back into the game, cutting Calvert's lead to 11 - 44-33 - with 6:51 left in regulation.
But Calvert answered the run when, after an offensive rebound from Danielle Kontak, Ritzler drained an open 3 to extend the Senecas' lead back to 14.
"We spent a lot of energy trying to come back," Frost said.
Calvert coach Tim Ritzler said his offense struggled a little bit after halftime.
"Everyone knows coming into the game that Kate's one of our top scorers, so we know that we're going to have to work to get her shots," he said. "In the first half we did a nice job setting some screens for her, get her some open looks, and she was knocking them down.
"North Baltimore's defense focused more on her in the second half, which allowed us to get more open shots for other people," Tim Ritzler said. "We missed, I thought, a lot of easy shots we did have. Those are some of the things we have to finish if we're going to beat some of the top teams in the league."
Olivia Frost led the Tigers with 20 points, and tied for the team lead with seven rebounds. Teammate Lacey Trumbull also had seven boards to go with four points.