Armstead was 5-of-9 and Lee was 5-of-13 from the field, and both were 7-of-8 from the free throw line in a game that NSU (14-11, 7-6 SLC) led every second. Kourtney Pennywell had 12 points and led the way with nine rebounds.
Lamar, who entered the game in a two-way tie for first place, fell to 14-10 overall and 9-4 in Southland Conference play.
The win snapped a 10-game losing streak to Lamar. NSU entered the game in a three-way tie for seventh place.
“I’m just so proud of these kids,” said an emotional co-head coach Brooke Stoehr. “They showed some toughness and grit and I am really, really proud of them.”
NSU led by seven points with 8:15 to play in the game, and Lamar put together a 9-2 run that tied the game at 55 with 5:35 to play in the game.
Armstead finished down the stretch with eight points, one block and one steal. Both Pennywell and Lee finished the stretch with two points apiece.
“That’s one of the things I love about this team. Sometimes they are so quick to forget things whether bad or good,” said Stoehr. “They tied it up and we could have easily folded and we come down and answered.”
After the Lady Cardinals tied the game, the Lady Demons missed a shot and set up for a charge on the other end to force a turnover.
Armstead scored a layup on the ensuing possession.
“There were a lot of times when we could’ve fouled and they fought through,” said the second-year coach.
Northwestern State finished the game 21-of-44 from the field and only 2-of-16 from behind the 3-point line.
Its defense held Lamar to 38 percent (24-63) from the field and 5-of-24 from long range.
Both teams struggled to hold on to the ball with 21 turnovers from Northwestern State and 20 by Lamar. The Lady Demons were able to gain 30 points off of turnovers, four more than the Lady Cardinals.
LU outrebounded NSU 37-35 and scored 15 second-chance points on 17 offensive rebounds. Northwestern State had 10 offensive boards.
Presley Owens had nine points, Janelle Perez had five, Emily Spector had four, and Chelsea Rogers had three on a 3-pointer.
Armstead had six rebounds and Owens, Rogers, and Meredith Graf had five boards.
Dominique Edwards and Shauna Long led LU in points with 15 apiece.
Gia Ayers, who fouled out with 25 seconds left, had 13.
Edwards had a double-double with 13 rebounds and Alice Robinson had 11 boards.
Northwestern State has Thursday night off and return to the floor for a 4 p.m. tip at Stephen F. Austin on Saturday.