THE Mittagong Lions under-18s have booked their place in the 2015 grand final.

The Lions advanced straight to the Group 6 under-18s division two decider with a 42-14 win over The Oaks Tigers on Saturday.

Mittagong overcame a horror start to record a commanding win at Sid Sharpe Memorial Oval, Oakdale.

Todd Mellish suffered a dislocated knee in the second minute of play.

The accident led to a long break in play before an ambulance arrived for Mellish.

The Lions failed to get momentum in the first half and trailed at the half-time break.

A stronger Mittagong outfit returned to the field in the second half and the visitors scored some late tries to round out the 28-point victory.

Lions coach Cameron Arlington said the Tigers put up a strong challenge.

"The scoreboard didn't do the game justice," he said.

"We were flat in the first half and I think the boys were shaken up by Todd's injury.

"The intensity didn't come back until the second half."

Arlington said Mittagong's standout performer was fullback Ben Powell.

However, he said the Lions were strong across the board.

"I am pleased with the way the boys did come back," Arlington said.

"They team lifted for Toddy."

The Lions will now head back to the training track and prepare for the Group 6 grand final on September 13 at Campbelltown Stadium.

Mittagong will either meet The Oaks or City, with those two teams to meet in a preliminary final this Sunday.