Williams started the overtime with four straight points. Camille Little answered with a basket with 3:15 left, but Connecticut only made two free throws the rest of the way.
Odyssey Sims added 19 points for Tulsa (13-14) and Vicki Baugh had 14. Sims, Williams and Christmas scored all 12 overtime points for the Shock.
Williams hit a long jumper with 25 seconds left in regulation for a 72-70 lead. After Connecticut's Shekinna Stricklen tied it with a layup, Sims had a runner roll out at the buzzer.
Jennifer Lacy led Connecticut (12-13) with 20 points, her second straight 20-plus game. Kelsey Bone added 14 points and Stricklen 13. Alex Bentley scored seven of Connecticut's first 12 points but she came down wrong on a 3-pointer at the 3:48 mark of the first quarter and did not return.