The Chippewas (19-13) opened the extra period on a 7-0 run and led the rest of the way. Williams made a pair of free throws with 17 seconds left to make it 79-74 and Central Michigan held on to advance to a quarterfinal matchup with No. 1 seed Buffalo.
Central Michigan had the largest lead of the final 10 minutes of regulation at 54-50 with eight minutes to go. It went back-and-forth from there with Shawn Roundtree's jumper with 40 seconds left tying it at 65 and forcing overtime.
Luke Meyer had 16 points, Roundtree added 15 points, Kevin McKay scored 14 and David DiLeo 12 with 10 rebounds for the Chippewas.
Justin Turner and Antwon Lillard had 17 points each and Daeqwon Plowden chipped in 11 for the Falcons (16-16).
Akron 79, (at) Western Michigan 78: Daniel Utomi had 26 points and freshman Virshon Cotton scored five of his 21 points in the final 45 seconds for Akron. Utomi was 9-of-12 shooting, including 6 of 9 from 3-point range, and Cotton had season-high-tying seven assists.
The 11th-seeded Zips will play No. 3 seed Eastern Michigan in the quarterfinals Thursday. Akron lost its only other matchup this season with the Eagles 63-49, its lowest scoring output since Dec. 16, 2014.
Cotton hit his fourth 3-pointer to give Akron (14-17) a seven-point lead with 45 seconds left, but Reggie Jones was fouled on a 3-point shot and hit all three free throws and then Thomas Wilder's steal and layup trimmed WMU's deficit to 77-75.
After a steal by Josh Davis, Bryce Moore banked in a tightly-contested 3 that gave the Broncos a one-point lead with 17 seconds remaining. Cotton, driving the right side of the lane, was fouled with 1.7 second left and hit both free throws and Akron held on.
Wilder had 21 points and seven assists and Jones scored 18, including four 3-pointers, for No. 6 seed Western Michigan.
Eastern Michigan 84, (at) Northern Illinois 77: No. 9 Eastern Michigan held No. 8-seeded Northern Illinois without a field goal for the final four minutes to oust the Huskies from the first round of the MAC tournament.
Danielle Minott and Courtnie Lewis each had 22 points and Micah Robinson scored 15 points for Eastern, which will face Central Michigan in the quarterfinals at noon Wednesday in Cleveland.
With the win, Eastern registered its seventh tournament win over a better-ranked opponent in program history, and its first since 2016.
(At) Western Michigan 85, Bowling Green 71: Jordana Walker had 32 points and Breanna Mobley and Deja Wimby added 22 and 21, respectively, to lead Western past Bowling Green in a first-round game of the MAC tournament.
The Broncos advance to play Ball State Wednesday at 7 p.m. in Cleveland.
MAC MEN'S TOURNAMENT
Game 1: No. 8 Central Michigan 81, No. 9 Bowling Green 77 (OT)
Game 2: No. 5 Kent State 61, No. 12 Northern Illinois 59
Game 3: No. 7 Miami 68, No. 10 Ohio 55
Game 4: No. 11 Akron 79, No. 6 Western Michigan 78
Game 5: No. 1 Buffalo (23-8, 15-3) vs. Central Michigan, noon
Game 6: No. 4 Ball State (19-12, 10-8) vs. Kent State, 2:30
Game 7: No. 2 Toledo (21-10) vs. Miami, 6:30
Game 8: No. 3 Eastern Michigan (20-11, 11-7) vs. Akron, 9
Game 5 winner vs. Game 6 winner, 6:30 (CBSSN)
Game 7 winner vs. Game 8 winner, 9 (CBSSN)
Semifinal winners, 7 (ESPN2)
MAC WOMEN'S TOURNAMENT
Game 1: No. 9 Eastern Michigan 84, No. 8 Northern Illinois 77
Game 2: No. 5 Ohio 85, No. 12 Akron 73
Game 3: No. 10 Kent State 80, No. 7 Toledo 76, OT
Game 4: No. 6 Western Michigan 85, No. 11 Bowling Green 71
Game 5: No. 1 Central Michigan (25-4, 17-1) vs. Eastern Michigan, noon
Game 6: No. 4 Miami (20-9, 12-6) vs. Ohio, 2:30
Game 7: No. 2 Buffalo (25-4, 16-2) vs. Kent State, 6:30
Game 8: No. 3 Ball State (24-5, 13-5) vs. Western Michigan, 9
Game 5 winner vs. Game 6 winner, 11 a.m.
Game 7 winner vs. Game 8 winner, 1:30
Semifinal winners, 11 a.m. (CBSSN)