CHICAGO - Ignited by a 40-point eruption from Sammy Mejia, DePaul blew open a tight game after halftime Friday night while handing Northwestern State its worst loss in 77 games, a 97-67 blowout. Northwestern (5-6) led much of the first half, when there were four ties and nine lead changes with both teams displaying hot shooting. But DePaul (9-5), winning its fifth straight, moved ahead 46-42 at halftime and opened the second half with a devastating 22-5 run over the first eight minutes. NSU, playing without its injured leading scorer Trey Gilder and suffering another ankle injury to senior forward Jermaine Spencer just before halftime, never got closer than 17 points afterward. "It was a matter of aggressiveness. They had a lot, we had very little in the opening stretch of the second half," said eighth-year Demons` coach Mike McConathy. "We`ve been giving up too much in transition all season and that was a glaring problem after halftime. We did a good job attacking the basket and attacking the glass in the first half but not afterward." Northwestern shot 47 percent in the first half but only 28 percent after, finishing at 37 percent. DePaul connected on 59 percent by halftime, 50 percent afterward and 54 percent overall. The Blue Demons took control inside the paint after halftime, outboarding the visitors 29-22 for a 45-38 advantage on the night. It was the worst defeat for the Demons since a season-opening loss at Oklahoma State three years ago. The previous worst margin since then was just 16 points earlier this season at No. 8 Marquette. Last year`s NCAA Tournament team was never defeated by more than 13. Mejia had 27 by halftime, hitting 13 of 16 shots, and seemed a threat to top basketball legend George Mikan`s school record of 53, but left the game after nailing 17 of 24 shots in 32 minutes. He drained 5 of 7 of his 3-point tries but only made 1 of 3 free throws. "He was sensational," said McConathy. "He made it when we guarded him, he created opportunities that he converted, he hit some tough shots and he made us pay when we left him uncovered on the perimeter. We tried a bunch of different things which worked pretty well on the rest of their players for the first half, but it had no impact on his game." Northwestern led by as many as eight points in the opening half despite Mejia`s performance. DePaul took the lead for good with 1:38 left before halftime. "We did a lot of good things until halftime," said McConathy. "We didn`t have the same ferocity going out there for the second half and we didn`t get some shots to fall that were going in earlier. We could have staved it off with a better defense but you have to give DePaul credit for doing a great job putting down the hammer." The Demons got 10 points by Spencer before his injury and a season-high 10 from Gerrell Thomas, along with 10 assists by Kennan Jones. Spencer missed the last two games with a bruised Achilles` heel but this injury seemed to be in the ankle area, said McConathy. NSU stays in the Chicago metroplex for a Sunday afternoon visit to the Big Ten`s Northwestern (9-3).