Tanisha Wright added 13 points and Sue Bird had 12 points and 11 assists as Seattle (8-1) won its fourth straight game and improved to 6-0 at home. The Storm boosted its Western Conference lead to four games over second-place Phoenix (3-4) and Tulsa (3-4).
DeWanna Bonner and Taylor Lilley scored 12 points and Diana Taurasi 11 to lead the Mercury.
"I don't see them losing another game the rest of the season, really," Taurasi said. "They're really good right now. They've got a lot of people doing a lot of good things."
Jackson scored nine points, Little seven and Wright six as the Storm outscored the Mercury 37-13 in the third quarter to help the Storm build a 87-48 lead. Seattle pushed the lead to 41 points early in the fourth quarter, when both teams played mainly reserves.
"We were just clicking," Bird said. "Everything seemed to go well for us whether it was defense, getting steals, forcing turnovers and getting rebounds. On offense, everybody was hitting shots and we were finding the open player and making it easy on ourselves."
The Storm led 50-35 at halftime after Phoenix had cut a 28-14 deficit late in the first quarter to five points. Cash scored 11 while Bird and Little each had nine in the first half.
"They're the No. 1 team and we got our butts kicked," Mercury coach Corey Gaines said. "We cut it to five and it's a different game going into the half."
Taurasi shot 3 of 11 from the field, including 1 of 7 on 3-pointers.
Seattle won 79-75 at Los Angeles on Saturday night.
"We had the game (Saturday) at 8 and tonight at 6 so we had less than 24 hours and that's a way for you to make an excuse and say we're going to be tired," Cash said. "A lot of people probably didn't expect us to come out and have the performance we had tonight. But this is a statement game for us, not so much for everyone else, just to say we're a veteran team and we come out and play hard."