Johnson tied Kelly Coppedge for second on Maryland's career goals list.
The senior Tewaaraton Award watch list nominee needs one score to claim sole possession with 220 goals.
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The Terps (11-2) outscored Penn 7-3 in each half. Maryland took a 2-0 lead, scoring the goals 34 seconds apart, by Johnson and Katie Schwarzmann (Century). The Quakers (5-3) answered with two of their own to tie the score with 23:50 left in the first half.
Maryland then went on a 5-0 run, including two by Johnson, to take the lead, 7-3.
In the second half, Penn would get as close as three goals before Maryland went on 6-0 run to keep the Quakers at bay.
Alex Aust continued her recent dominance with a nine-point showing via three goals and a career-high six assists.
"We did a nice job today working together all over the field," coach Cathy Reese said. "We fought hard to come up with draws and create scoring opportunities."
Brittany Dipper led the Terps with seven saves.
Maryland's defense held its fourth straight opponent to eight or fewer goals.
The win marks the second straight for Loyola (6-3, 2-0 Big East). The Bearcats fell to 3-5, 0-2.
The Bearcats became the seventh team to score first against the Greyhounds this season, but Loyola responded with a seven-goal run to take the lead by the 14:02 mark. Paton and Hannah Schmitt (John Carroll) each notched two goals in the run. Loyola fell behind 1-0 before scoring seven straight.
Quinnipiac 12, Mount St. Mary's 10: The visiting Mount (3-8, 2-1 Northeast Conference) led 7-4 early in the second half before the Bobcats (4-4, 3-0) reeled off seven straight goals to pull ahead.
Mount St. Mary's answered with a three-goal rally late in the second half, with Kaitlyn Larrimore scoring twice, but the comeback bid fell short.
Erin Seipp (Notre Dame Prep) paced the Mount with four goals and an assist. Marissa Caroleo had three goals and an assist for Quinnipiac.
No. 3 North Carolina 4, No. 8 Duke 2: The host Tar Heels (11-1, 3-0 ACC) took the lead for good seven minutes into the second half. The Blue Devils fell to 8-5 and 2-1.
Becky Lynch had a goal and an assist for North Carolina.
No. 6 Notre Dame 13, Rutgers 12, OT: Trailing 12-11 with a minute left in overtime, the visiting Fighting Irish (8-0, 2-0 Big East) scored twice in 30 seconds to beat the Scarlet Knights (5-4, 0-1).
Maggie Tamasitis assisted on both overtime goals by Margaret Smith (McDonogh) and Jenny Granger.
No. 15 Massachusetts 15, Richmond 14, 2OT: After trading goals in the first overtime, the visiting Minutewomen (10-1, 1-0 Atlantic 10) won on Tanner Guarino's goal with 21 seconds left in the second overtime.
The Spiders fell to 4-6 and 0-1.