It was one of the few highlights for shorthanded Harrodsburg (7-4), which was no match physically for Holy Cross (11-0).
"They were the biggest team by far that we've faced all year long," Harrodsburg assistant coach Keith Brown said.
Dunn scored on a 5-yard run early in the second quarter to pull the Pioneers within 7-6, but Holy Cross took control after that.
Holy Cross used a balanced rushing attack to grind out 186 yards on the ground, and the Cougars threw for another 173 yards.
Quarterback Nick Nail ran for two touchdowns and completed six of seven passes to lead the Cougars.
Harrodsburg was without three starters on defense - David Hunt and Shane Webb sat out with injuries and Mariqus Brown also did not play - leaving the Pioneers with six first-year starters, including three freshmen.
"After a while they just started to whip us," Yeast said. "We really just couldn't stop them. They're just too big and strong in the backfield and on the line."
Dunn started the game at quarterback in place of Brown, and he completed all three of his passes for 16 yards. Freeman Edwards was 3-for-9 for 33 yards.
Harrodsburg had 216 yards rushing, led by Cory Jackson with 123 yards on nine carries.
Dunn needed about 30 yards to break the rushing record in the fourth quarter, by which time the outcome had been decided.
He left the game with a stinger 3 yards short of the record, then returned on Harrodsburg's next series and lost 5 yards on his first play.
But after Dunn's 14-yard gain put him over the top, officials stopped the game to award the game ball, and Holy Cross' public-address announcer acknowledged his achievement.
"I was really appreciative of them to be able to stop the game," Yeast said. "At that point things were not going the way we hoped, but that was certainly a bright spot."
Dunn left the game for good after that play, and Jackson ran for a 38-yard touchdown on the Pioneers' next play.
Fleming County 42, Mercer County 35
At Flemingsburg, Andrew McCloud's best game wasn't enough to keep Mercer County alive as Fleming County defeated the Scotties 42-35 Friday in the first round of the Class AA, Region 3 playoffs.
McCloud broke his own single-game school rushing record and scored all five touchdowns for Mercer (5-6), but Fleming (8-3) got the last two scores to erase the Scotties' 35-28 lead in a game which neither team led by more than seven points.
"It was a great game to watch," Mercer coach Duane Hammons said.
McCloud ran for 350 yards on a career-high 38 carries, surpassing the school record he set three weeks earlier with 338 yards on 24 carries against Henry County.
"Good players make good plays. He really showed up when the going got tough," Hammons said.
McCloud, who was voted the District 5 player of the year last week by the district's coaches, accounted for most of Mercer's offense. The Scotties rushed for 359 yards and threw for 70.
Fleming rolled up 489 yards.
Mercer started the slugfest by scoring on the second play of the game, and the teams traded scores until Fleming got two in a row to take a 28-21 lead, which Mercer erased in the final minute of the first half.
The Scotties then broke the halftime tie by scoring on their first possession of the second half, but they would not score again.
Fleming tied the game late in the third quarter, after which Mercer missed a 41-yard field goal and failed to convert on fourth-and-inches from its own 15-yard line thanks to a fumbled snap.
"They hadn't stopped us yet," Hammons said. "That was going to be a big momentum switch right there."
The Panthers later got the go-ahead score after an interception ended Mercer's next series.
Mercer got the ball back on the Fleming 45 with about a minute left after a long punt return, but a short pass to McCloud ended in a fumble that sealed the Scotties' fate.