"Amazing," Elwood's senior running back said after a 34-carry, 350-yard, five-touchdown performance made him Indiana's career high school rushing leader and helped the Panthers to a thrilling 49-42 victory against rival Alexandria.
Former record holder Otis Shannon, who starred at Cathedral from 1997-2000, stood on the sideline and cheered Mireles' every rushing attempt.
The Elwood star broke the record on a 24-yard carry late in the third quarter. He capped the drive with a 2-yard touchdown run to cut the Panthers' deficit to 34-30.
Shannon said there was nothing bittersweet about watching his record fall.
"Not at all," he said. "I'm actually excited. Just to even have a record in any state, let alone Indiana with all the tradition and great athletes we've had here, it's beyond cool to have somebody break a record of yours that's an all-time record. Hopefully, he'll take it over 8,000 (yards) and take his team to a championship. And then he can come back and give a ball away like I did to the next kid who breaks the record."
Mireles wasn't the only record breaker on the evening.
Alexandria quarterback Blaize Kelly completed 41 of 57 passes for 334 yards and three touchdowns, becoming the Tigers' all-time leading passer in the process.
Kelly set the school record on a 29-yard touchdown pass to Mason Hoke that tied the game 21-21 with 39.8 seconds left in the first half. Hoke had an outstanding game of his own with 14 receptions for 166 yards and two scores.
Elwood rallied to take the lead on a 27-yard field goal by Anthony Bennett as time expired for the half.
But Alexandria (6-3, 4-3 Central Indiana Conference) answered with touchdown runs of 20 and 3 yards by Evan Hodges to start the third quarter and move in front 34-24.
Mireles' touchdown on the record-breaking drive got the Panthers back into the game, and his 2-yard score with 1:30 remaining in the third quarter put Elwood (6-3, 6-1) ahead for good at 37-34.
Mireles added touchdown runs of 8 and 39 yards in the fourth quarter as the Panthers' lead expanded to 49-34.
Elwood also got a big defensive play from Griffin Hughes, who intercepted Kelly in the end zone on a pass from the Panthers' 11-yard line to kill a key drive.
Alexandria's Bryan Carter scored on a 6-yard run with 13.1 seconds left in the game, and Kelly hit Jonah Jerrils for the 2-point conversion to pull the Tigers within seven.
But Elwood recovered the on-side kick, and quarterback Alex Mireles took a knee to run out the clock.
"We kind of anticipated a track meet going in, and I think people got their money's worth," Elwood coach Marty Wells said. "It was a great night for Sammy, a great night for the team, a great night for our school and a great night for the community."