Going into its Southern Section Division I semifinal against Encino Crespi, Coach Tom Hoak admitted that No. 1 Rialto Eisenhower was looking past the Celts.
"Maybe we were thinking too much about playing for the championship," Hoak said.
Crespi led at halftime and nearly pulled off a huge upset before losing, 7-3, Saturday night before 6,000 at Eisenhower.
The Eagles (13-0) will meet Mater Dei in the final Friday night.
Running back Marlon Farlow scored the game's only touchdown in the third quarter on a 19-yard run.
The Celts then drove to the Eisenhower six-yard line, but defensive back Bennard Hadnot intercepted a pass by Crespi's Dave Lins at the goal line to preserve the victory.
"That interception will go down as the play of the season," Hoak said.
Saturday's gutty, aggressive effort will definitely go down as the game of the season for the Celts (8-5), despite the loss.
"It's just incredibly disappointing," said linebacker Patrick Jeffries, who led Crespi's swarming, undersized defense. "I just wish we could have shut them out, 3-0."
At halftime, that appeared to be a possibility.
The Celts scored on a 34-yard field goal by Mark Herz only 14 seconds before halftime.
Herz scored on a free kick, which Crespi opted to take after Vito Clemente made a fair catch at Eisenhower's 24-yard line.
Eisenhower defenders had to stand 10 yards off the line of scrimmage and could not rush Herz, whose kick stunned a team that is ranked second in the nation by USA Today.
The Celt defense shut down the Eagle offense in the first half.
But in the third quarter, Eagle receiver Demond Birks turned a short pass into a 43-yard gain and Farlow scored on the next play.