Early stages of the match saw both sides come within striking distance of putting the first points on the board through penalty goals but both kickers failed to direct the ball through the posts.
It was the Blues who landed the first blow with Brennan Czinner crossing in the corner.
The conversion was missed and five minutes later the Barbarians hit back to find themselves two points in front when a barnstorming Keith Ellis carried defenders over the line for his five-pointer.
Cody Graham crossed the white stripe out wide shortly before half-time to extend the Baa Baas' lead to 14 points to five.
The Blues found their rythym after the break and scored a penalty goal two minutes in.
They closed the gap in the scoreline when Mike TeMoana sliced through the opposition's defence to score next to the posts.
Another penalty goal to the Blues had them with their nose in front but that was short lived when the Barbarians managed to slot one of their own to put them back in front 20-18.
The Blues threw everything they had at the Baa Baas in the final stages of the match but the Barbarians' defence held them out and eliminated any chance of the Blues claiming their fourth straight title.
Coach Tom Bower said the tight finish had him on the edge of his seat he was pleased his side's defence held up to the Blues' attack late in the match.
"It was heart attack kind of stuff," he said.
"It was very back and forth.
"Right until that last moment, you never know.
"Especially with them on the attack.
"Everyone was heart in mouth but I backed the boys' defence and they came through with the goods today."
Barbarians' captain Luke Heagney said toppling St Albert's in the grand final will be the ultimate test but believes his side have what it takes.
"It has been a long time since the Baa Baas have been in the final," he said.
"We have had a pretty up and down season but we are coming good when it counts.
"Albies are a very, very good team.
"We are just going to have to give it everything we have got to try and beat Albies.
"Hopefully we can get the job done."