They ran out 50-46 winners.
This set up the last game as a decider, and Southern made a good start, leading 13-12 at quarter-time and eventually getting a five-goal advantage in the second stanza.
However, Northern clawed their way back and took a 38-36 lead into the final break.
Southern came roaring back to take a seven goal advantage and while Northern made a recovery, they ran out of time to be beaten 47-44.
Metropolitan were not as strong a team as the 2014 squad because while the matches were a pointer towards the upcoming Wanganui representative team, head coach Lisa Murphy already has 20 names of players who will have a separate trial on Thursday.
"But the thing I'm looking at today is are there any others that haven't put their names down," Murphy said at the stadium.
"It's going to be interesting to see how we go - it's been 10 years since we've had a representative team." Murphy hopes to name her finalised squad by this weekend.
They will travel to Wellington to play a pre-national tournament on September 12.
She said the tournament will include the representative squads from most of the smaller centres from the Central Zone, who will then go on to play at the 2015 Lion Foundation Netball Championships.
"It will be nice to have that little taste." Wanganui will then enter the national tournament at the ASB Sport Centre in Wellington, from September 28 to October 2.
The resurrection of the Wanganui senior team comes as Netball NZ has gone full circle by bringing back the national tournament between the various centres, rather than playing regional tournaments between teams selected out of five zones.