It was the sixth win in seven games for the Storm (7-8).
Tina Thompson had 20 points, seven rebounds and four blocks for Seattle and Sue Bird added 11 points, eight assists and five rebounds. Reserve Ewelina Kobryn scored 13 points.
The Storm played without starting center Ann Wauters (strained calf).
Asjha Jones had 15 points and 11 rebounds for Connecticut (10-4) and Kara Lawson scored a team-high 22 points.
Tina Charles, the Sun's leading scorer, had 13 points and 14 rebounds.
Katie Smith made a contested 3-pointer from the right corner with less than three minutes left in overtime to give Seattle a 79-78 lead.