The first half had ended, and Mundelein junior Sean O'Brien just didn't feel right. The Mustangs' second-leading scorer had no points and his team trailed 32-27 at halftime.
It was more than enough to make anyone in a Mundelein jersey a little queasy.
When the second half started O'Brien still was a little ill as the deficit grew. He needed a timeout and Mundelein took one.
When O'Brien came back after dealing with his problem in the locker room, it was Zion-Benton suddenly feeling ill.
O'Brien erupted for 9 points in the third quarter and 14 in the second half to help the No. 3 seed Mustangs overcome a 25-point, 13-rebound performance by sophomore standout Milik Yarbrough to defeat the host and No. 16 seed Zee-Bees 70-57.
Mundelein (24-7) will face No. 10 seed Lake Zurich, a 54-46 winner over Barrington in the regional final Friday night at Zion-Benton. Zion saw its seven game winning streak snapped and closed the year at 15-15.
"I think (Sean) just relaxed -- I think we were all a little too tense," said Mundelein coach Dick Knar. "We were passing up shots we don't normally pass on, and once we started to relax I think Sean and the rest of the guys started doing the things we needed to do."
Zion-Benton scored the first bucket of the third quarter to open a 34-27 advantage before a refreshed O'Brien and the Mundelein offense finally got into synch.
O'Brien contributed a steal and an assist. Then his hustle play led to a Nate Brune 3-pointer that tied things at 38-38 with 5:09 left in the quarter. O'Brien gave the Mustangs the lead for good on a pair of free throws and a layup. This all came as part of a 15-4 Mundelein run that froze Zion-Benton.
"I just couldn't find any kind of rhythm in the first half," said O'Brien, who also had 9 rebounds and 5 assists. "(Zion) was killing us on the boards and we came out kind of soft. In the second half we came out and worked harder on the boards."
When O'Brien heated up, so did the rest of the Mustangs. Robert Knar scored 8 of his team-best 17 points after half time and China Ebube (15 points) and Cliff Dunigan (14 points) also took advantage of the more aggressive play by Mundelein.
"I thought Mundelein came out and played a very good third quarter," Zion coach Don Kloth said. "I thought they rebounded exceptionally well and did a good job once they got the lead of holding it."
Curtis Cook, in his final game at Zion-Benton, finished with 15 points and 9 boards.