The Mustangs took an 18-16 lead with less than two minutes remaining on the clock when halfback Tyrell Scott finished off an attacking move.

However, the Blues earned possession from the resulting kickoff and elected to lock the scores up at 18 after they were awarded a penalty for a strip.

The Mustangs had an early attack in extra-time but weren't able to apply the killer blow.

The Blues didn't make the same mistake, capitalising on lazy defence around the ruck with an inside ball to centre Willy Baker, who grabbed his second of the afternoon.

The Mustangs threw everything at the Blues for the remaining six minutes of the extra period but they weren't able to crack the Blues’ defence.

Mustangs captain Jesse Douglas played a starring role in the contest. He saved two certain tries with terrific tackles before he shrugged off three defenders to run 30 metres and score to give the Mustangs a 12-4 lead with 15-minutes remaining.

However, Macleay Valley were competing in only their second match in five weeks and it played its part in the result.

The Mustangs tired in the final 15-minutes and allowed the Blues to hit back and take the lead 16-12 before Douglas' effort.

"It hurt us a little only having one game for a month before today but we still gave ourselves a chance to win," Mustangs U18.5s coach Richard Dixon said.

The side is expected to remain strong for next year with the majority of the team still eligible to compete in the U18.5s.

"They will give the premiership another crack next year," Dixon said.

"They all still had a great season, it is disappointing to lose but they have all developed this year and should be proud of themselves."

Dixon is undecided whether he will remain coach of the side next season.

It is the second straight year the Mustangs U18.5s have lost the grand final.