LOWELL — St. John’s Prep running back Johnathan Thomas stood on the sideline with his helmet in hand, waiting patiently as the last 4½ minutes ticked off the clock.
After all, he deserved the breather.
The junior piled up 173 rushing yards in the second half and scored three times, leading St. John’s Prep to a 21-0 win over Andover on Tuesday night at Cawley Stadium.
The fourth-ranked Eagles (10-1) advance to the Division 1 Super Bowl for the first time since 2010, and will play Brockton (9-3) Saturday at Bentley.
“It [felt] like the job was done,’’ Thomas said. “But it’s not done. We have to go to back to work and I’m ready for it.’’
Like a pair of emergency paddles primed for defibrillation, Thomas shocked the Eagles’ offense to life in the final two quarters.
After Andover running back Jack Sylvester (15 carries, 146 yards) put his team in position to score with a 64-yard run on the first play from scrimmage in the third quarter, the Eagles held, forcing the Golden Warriors to try a 31-yard field goal.
Freshman Oliver Eberth’s kick was short, and St. John’s Prep took over at the 21-yard line.
Thomas, who rushed for just 25 yards in the first half, powered a 10-play, 79-yard drive and put the Eagles on the board with a 1-yard run with 3:31 remaining in the third quarter.
On the drive, Thomas rushed nine times for 61 yards, with a facemask penalty early in the possession helping the Eagles’ cause.
“We started with one thing and when it was working we kept with it,’’ Thomas said. “We knew we had to get in the end zone and we’re a second-half team.’’
On the next possession, Andover quarterback CJ Scarpa (16 for 28, 162 yards) completed a 22-yard pass to Will Heikkinen to the St. John’s 11, but safety Alex Moore stripped the ball and recovered the fumble.
Starting at their 11, the Eagles turned to Thomas again. This time, he rushed for 69 yards, mixed in with a 20-yard reception by Jack Sharrio, and scored on a 19-yard run to put his team up, 14-0, early in the fourth quarter.
Andover was stopped on fourth down on its next possession, and the Eagles took over at the 50.
On the second play, Thomas escaped several Andover tacklers and broke for a 48-yard score on his final carry of the night.
“The last touchdown was just unbelievable,’’ said St. John’s Prep coach Jim O’Leary, who earned his 200th career win. “He just has to get to that first level and he’s gone.’’
Andover (10-2), which came in averaging 40.8 points per game, advanced to the red zone four times without getting into the end zone.
“We knew they had a great offense,’’ Eagles defensive back Lucas Bavaro said. “We let up a lot of yards, but that’s our defense. We bend but don’t break.’’