Westminster improves to 2-5 on the year and 1-0 in conference play, while the Griffins fall to 1-4 and 0-1.
"We came out with a great focus on the boards," said Westminster Head Coach Tracey Braden. "We talked about making a greater effort in 'sharing the love' and we believe we did that."
Zalis tallied a career-high 17 rebounds as part of her double double, along with a game-high 20 points. Johnson added 14 points and 11 boards.
The Blue Jays started out the game on a 7-0 run on layups from Kelsey Ray, Johnson, and a three-pointer from Zalis.
Westminster ended the quarter with a 23-14 lead, and never looked back. The Blue Jays pulled ahead by as many as 15 points in the second quarter, but ended the half with a 38-25 advantage.
With five minutes remaining in the third quarter, the Griffins were back within nine points of catching the Blue Jays. By the end of the third quarter, the Westminster lead had been reduced to 10.
The Griffins were able to keep the game close in the final 10 minutes, getting to within six points in the final minute. Ray and Johnson knocked down five freethrows down the stretch to ensure the Westminster victory.
"The energy from the bench was good," said Braden. "It came down to freethrows and boards tonight, and it was nice to get our first conference win out of the gate."
Ray added 17 points for the Blue Jays, while Brooke Stauffer added 10.
Westminster continues SLIAC play with a 1 p.m. matchup against Greenville Saturday.