Smith, holding state marks for career passing yards and touchdowns, broke a 14-14 deadlock with 5:29 left in the third quarter.
Earlier, Quinn Houser broke loose on a simple jet sweep to tie the game for Lancaster Catholic (15-1) just 20 seconds after Trent Hurley opened the scoring on a 7-yard keeper for WPIAL champion Greensburg Central Catholic (13-3) on a 12-play, six-minute opening drive. Jordan Stewart added another first-half score for the Crusaders with 5:31 left in the half.
"Stats don't really matter in a game like this. My hat's off to both teams," Lancaster Catholic coach Bruce Harbach said. "That first play was it. That really set an offensive tone for us."
Hurley scored twice for Greensburg Central Catholic, but the Bowling Green recruit mustered just four completions for 71 yards. David Miller carried 30 times for 104 yards for the Centurions (13-3), who were held to four first downs in the final 24 minutes.
"We would have liked to throw a little more, but I'm not making excuses for what was a great football game," Greensburg Central Catholic coach Muzzy Colosimo said. "I'm not going to apologize for losing to a football team that good."
Smith was held to 35 passing yards as Lancaster Catholic won its 13th straight, the Crusaders' only loss coming at the hands of Class AAA finalist Manheim Central.