Mendenhall rushed for two touchdowns, and Illinois (7-3, 4-2) pulled into sole ownership of third place in the Big Ten after racking up 655 yards on offense.
Up next is a trip to play top-ranked Ohio State, by far the biggest test for coach Ron Zook in this turnaround season by the Illini, who won one conference game over his first two years.
This wasn't much of a tuneup, though. Minnesota (1-9, 0-6) has yielded more yards than any of the other 118 teams in major college football, and this was as bad as the defense has been during this embarrassing season: the total package of missed tackles, loose coverage and no pass rush.
So much for the homecoming game.
Williams put the soft touch on his passes that he'll need if Illinois is going to have a chance against the unbeaten Buckeyes next week. His elusiveness and speed have never been in question, but accuracy has not been the sophomore's strong suit.
Williams completed a career-high 14 passes out of 21 attempts for 207 yards, the two scores, and one interception. He carried 18 times for 133 yards and one touchdown, too.
Adam Weber threw an interception on the first play from scrimmage, setting up Williams for a 47-yard touchdown pass to Jacob Willis on the next possession. Another perfectly thrown ball by Williams on the next series went for a 22-yard score to Jeff Cumberland, giving Illinois a 14-0 lead.
Zook didn't let up, either. The Illini had the ball at their own 37 with 30 seconds left before the half, and they hurried down the field for the first of three field goals by Jason Reda.
They kept the pressure on into the fourth quarter, when Mendenhall burst through the middle and shed several tackles on fourth-and-1 at his own 49 to gain 13 yards. He scored on a 33-yard run three plays later to make it 44-10 with 10:25 left.
Though he tried to shrug off the significance this week, Minnesota coach Tim Brewster was facing his alma mater -- the school he had 64 catches and 688 yards for as a senior tight end in the 1983 season that finished with a trip to the Rose Bowl.
The Gophers are a long, long way from there, despite Brewster's promise to take them there eventually when he succeeded Glen Mason this winter.
Weber completed 18 of 31 passes for 208 yards. He rushed for one score and passed for another. Using a spread scheme that doesn't drain the clock like the power running attack did under Mason, the depleted defense was worn out even more.