Earlier this week, Winthrop (19-6) defeated Cohasset (22-3) 58-55 to capture the Division 4 title at TD Boston Garden to begin championship festivities.
Senior center Anthony Hatzisavas led the team with 16 points.
Junior forward Joe D'Amore chipped in 15 points, including 11 in a hotly contested fourth quarter which saw Cohasset charge back from nine down with 2:30 to play.
For Winthrop, a town 20 minutes east of Boston, the championship victory came after three consecutive losses in the north sectional finals.
Cohasset, a coastal town twenty minutes southeast of Boston, was led by sophomore Shane Haggerty with 17 points.
Kyrel Jaundoo and Sam Richardson also registered double-digit point totals in the losing effort.
Three additional state championships will be decided Saturday at the DCU Center in Worcester.
The Division 1 title game features the St. John's Pioneers (21-5) versus the St. John's Prep Eagles (25-1). The Eagles enter the championship game with only one loss and the top ranking in Massachusetts. Their national ranking sits in the 40's.
St. John's Prep is led by senior small forward Pat Connaughton, a Notre Dame recruit and MaxPreps top 100 player.
The New Mission Titans (19-4) will face the Northbridge Rams (18-5) in the Division 2 final.
Northbridge, seeking its first every state title, is led by senior guard Corey Pryor who averages 27 points per game on the season.
New Mission holds a tremendous size advantage entering the game with a starting lineup averaging 6-foot-4.
In Division 3, the Watertown Red Raiders (17-5) are a slight favorite over Whitinsville Christian (19-2).
Watertown is led by senior guard Marco Coppola who has averaged 23.5 points per game in the playoffs and led Eastern Massachusetts in scoring this season.
Whitinsville Christian has relied on their size advantage to disrupt state tournament opponents en route to the title game.
Guard Taylor Bajema enters the final on a hot streak averaging 21.3 points per game in his last three.
Massachusetts at a Glance - All Games ET
Saturday, March 19 @ DCU Center in Worcester
Division 3 Finals
12:30 p.m. - Watertown vs. Whitinsville Christian
Division 2 Finals
4:00 p.m. - New Mission vs. Northbridge
Division 1 Finals
7:30 p.m. - St John's vs. St. John's Prep