The speedy Sooners (2-0) used a trapping defense to harass the Leathernecks into 23 turnovers and several long stretches without a basket, including during a 15-0 run to open the game.
Lyndsey Cloman added a career-high 13 points and freshman Aaryn Ellenberg also scored 13 as the Sooners won their home opener for the 13th straight year. It was just the fourth time Oklahoma won its first home game by 40 points or more.
Erica Lewis led Western Illinois (0-2) with 13 points, with nine coming from the free-throw line.
The Leathernecks had only two baskets in a 12-minute stretch in the second half and were outscored 23-5, falling behind 75-34 on Ellenberg's jumper from the right side with 5:49 to play.
Oklahoma played much of the final 8 minutes with four freshmen on the floor and still managed to build on its lead.
The Sooners forced 33 turnovers in their season opener after amassing 80 takeaways in two exhibition games, and continued to add to that total.
Western Illinois had already missed its first six shots and committed six turnovers before it finally cracked Oklahoma's defense. The Sooners scored the first 15 points of the game and were up by 20 within the first 10 minutes against the Leathernecks, who were among the eight lowest-scoring teams in Division I last season.
Anne Borgertpoepping had Western's first basket with a left-handed floater with 6:42 gone in the first half.
When the Sooners finally allowed six straight points, they responded by forcing Western Illinois into turnovers on six of the next seven possessions and held the Leathernecks without a basket for another 4 1/2 minutes.
Robinson, a preseason All-America selection, turned three steals into fast-break layups during that span and pushed the lead to 42-16 on the last one.