Delia Cox, who finished with three goals and three assists, had two goals and an assist as the Terps took a 4-0 lead.
The Wildcats closed the half with a 7-0 run to take a 7-4 halftime lead.
"I thought we came out with great intensity and were very smart with the ball," Terps coach Cindy Timchal said.
"They then frustrated us a bit with their defense and got on a little bit of a roll and made it tough to come back. They are a great team, but I thought we really fought hard and competed."
Maryland pulled within one with 26 minutes left in the game after Cox scored unassisted a minute into the second half and assisted on Kelly Kasper's goal.
The Terps won the ensuing draw, but were unable to capitalize on the possession. The Wildcats pushed their lead to 9-6 after Laura Glassanos scored twice within 17 seconds.
Casey Magor won the next draw, and Krista Pellizzi's goal made the score 9-7. Maryland won the next draw but turned the ball over in the offensive end. Lindsey Munday scored a free-position goal at 17:42 to give Northwestern a 10-7 lead.
Pellizzi scored her second goal to pull the Terps to 11-8 with more than 13 minutes left.
Northwestern controlled possession the rest of the way.
Allie Buote, making her first start, made nine saves for the Wildcats. Lauren Cohen had three caused turnovers on defense for the Terps.
Northwestern 7 6 - 13
Maryland 4 4 - 8
Goals: N-Kjellman 3, Glassanos 3, Josephs 2, Frank 2, Albrecht, Munday, Nielson; M-Cox 3, Kasper 2, Pellizzi 2, Magor. Assists: N-Kjellman 3, Albrecht, Glassanos; M-Cox 3, Magor. Saves: N-Bangser 2; M-Buote 9. A: 231.