Prospect's football team left the field of its George Gattas Stadium with a 13-0 lead at halftime on Friday night.
The Knights' marching band never got on the field at intermission due to the threat of rain.
Then Glenbrook South really asserted itself on the field in the second half.
The Titans rallied for 27 unanswered points to capture a 27-13 triumph in the nonconference season opener on a humid night in Mt. Prospect.
"We knew we wanted to play at a fast pace all night," said Glenbrook South coach Mike Noll. "Because then we knew we had a chance to win in the fourth quarter. We don't have platoons. We don't have any players going both ways on the field."
The Titans had senior tight end Sean McDonagh going to the end zone three times in the second half. All three of his receptions (36, 15 and 18 yards) were for touchdowns, the third putting the visitors ahead 20-13 with 9:23 left in the game.
McDonagh's third grab was set up by Carlos Benitez' 17 yard interception return to the Knights 18-yard line.
It took just one play for 6-foot-7 QB Fitz Stadler to find the 6-4 McDonagh across the middle for the 18-yard score to make it 20-13.
"That's the kind of play we practice a lot," Benitez said of his game-changing interception. "We had a great rush by the d-line and we executed."
The Titans' defense forced three-and-outs on Prospect's next two possessions.
The second time, South took over at the Knights' 39 yard line and needed one play to score on Ryan Janczak's 39-yard run around right end with 1:42 left in the game.
"Give Glenbrook South credit," said Prospect coach Mike Sebestyen. "They keep coming after you. We'll be better next week.
"We have to continue to play football and in the second we didn't. That's my fault. We played 24 minutes and you've got to play 48."
In the first 24 minutes, the Knights were in command.
Prospect senior Vincent Lai had two big fumble recoveries, and both led to touchdowns for the Knights.
The first one (at the Knights' 29-yard line) was followed by sophomore Andrew Shafis' 71-yard TD run on the very next play that gave Prospect a 7-0 lead with 4:59 left in the first quarter.
The second recovery came on the Titans' next drive, and gave the ball to the Knights at South's 39.
Running behind lineman Jackson Doughty, Vinny DiFatta, Luke Wrede, Billy Matzek and Matt Schultz, Lai followed with runs of 18 and 15 yards, setting up junior Matt Drew's 6-yard TD pass to Anthony Bongiorni with 45.9 seconds left in the first quarter for the 13-0 lead.
"I thought Vinny (Lai) did a nice job running the ball and playing defense," Sebestyn said. "And Shafis, for a 15-year-old sophomore, did a heck of a job running the ball. I like our running back and receivers combination.
"We are a good football team. We just have to finish. We've got to take care of some details to do that."
At halftime, Noll told his team it just had to focus on playing better football.
"We had 4 fumbles, 4 penalties and 2 turnovers (in the first half)," he said.
The Knights defense could take credit for much of that.
"I thought our defense did a great job," Sebestyn added. "Offensively, we moved the ball in the first half but then we put our defense in a bind when we didn't move it in the second half."