Green Island performed the Houdini act at Miller Park, scoring two tries in the last three minutes to beat Alhambra-Union by a point.
The first try, after 37 minutes in the second spell, came from a drive from a lineout followed by two phases, before experienced halfback Dean Moeahu scored wide out. He converted the try.
The last try was even more impressive and began as a counter-attack on Green Island's own 22m.
Fullback Jesse Toto sped up the left flank, and he handled the ball two more times before scoring the winning try wide out.
Alhambra-Union had a stronger pack and led 14-5 at the break and looked to have the win sewn up when it led 21-10 midway through the second spell.
It had the stronger scrum that pushed Green Island back on a few occasions and hooker Liam Coltman took two tightheads.
Alhambra-Union had a better balanced lineout with flanker Vaughn Bruce taking ball at the back and captain Matt Kissick was dominant at the front.
First five-eighth Peter Breen had a sound game and kicked accurately for the corners and landed conversions for the three tries.
Moeahu was the kingpin for Green Island, with his astute reading of the game. His quick and long passes gave space to his outsides.
Hanipale Galo always threatened to break the defensive line and Toto punted long and accurately and was dangerous when entering the line.
Aggressive flanker Mika Mafi was the best of the forwards and No 8 Josh Beer was powerful on the drive.
- Green Island 22 (Jesse Toto, Josh Beer, Dean Moeahu 2 tries; Moeahu con), Alhambra-Union 21 (Percy Stephens, Ben Qauqau, Vaughn Bruce tries; Peter Breen 3 con). Halftime: Alhambra-Union 14-5. Referee: Ben O'Keefe.