No. 1 Archbishop Spalding (10-2-3, 5-1-2, Interscholastic Athletic Association of Maryland A Conference) took a 3-1 lead, but host Mercy (9-7-1, 2-5-1) scored twice in second half to force overtime and an eventual stalemate.
Spalding's Maria Kiskis scored twice, at the two minute and 57-minute marks.
"Based on our past experience with this team, this was a winnable game," Spalding coach Ashly Kennedy said. "Give a ton of credit to Mercy for their fight."
Spalding secured the top seed in the upcoming conference playoffs and gets a first-round bye before playing Nov. 3.
Mount de Sales 1, Severn 1, 2OT: Michelle Money gave the Admirals (11-7-2, 9-2-2 IAAM B Conference) a 1-0 lead 16 minutes into the first half before Madison Berry scored the equalizer four minutes later for the host Sailors (9-6-1, 8-4-1).
Neither team capitalized on chances in the second half.
Glenelg Country 1, Catholic 0, 2OT: Addie Schmidt scored the game-winner assisted by Kiersten Moore as the Dragons (5-7-1, 5-7-1 IAAM B Conference) beat the host Cubs (2-14-1, 1-11-1).
Garrison Forest 5, Friends 0: Kaylin Silva scored twice to lead the Grizzlies (9-6, 8-5 IAAM B Conference) past the Quakers (5-11-1, 2-10-1).
Garrison Forest plays in the first round of conference playoffs Friday.
Field hockey
No. 2 Archbishop Spalding 4, St. Mary's 1: Margot Lawn had a hat trick to lead the Cavaliers (17-3, 10-2 IAAM A Conference) past the host Saints (4-8-1, 3-8-1).
The win secured the top spot for Spalding. The playoffs begin Monday.
No. 6 McDonogh 1, No. 4 Notre Dame Prep 0: Frehsman Blake Cunneen scored the game-winner assisted by Emma Shettig as the host Eagles (12-4, 8-4 IAAM A Conference) upset the Blazers (12-4, 9-3).
Severn 1, St. Paul's 0: Marah Vain Callahan scored the game-winner on an assist from Kamryn Day to lift the host Admirals (6-8-1, 4-4 IAAM B Conference) over the Gators (4-7, 3-5).
Baltimore Sun Staff contributed to this article.